November, 2015

Does Dairy Cause or Prevent Cancer? An Objective Look

Cancer risk is strongly affected by diet. Many studies have examined the relationship between dairy consumption and cancer. Some studies indicate that dairy may protect against cancer, while others suggest that dairy may increase cancer risk. The most commonly consumed dairy products include milk, cheese, yogurt, cream and butter. This article reviews the evidence linking dairy products with cancer, looking at both sides of the argument.

How Do These Studies Work?

Before we continue, it is important to understand the limitations of the studies examining the link between diet and disease. Most of them are so-called observational studies. These types of studies use statistics to estimate the relationship between dietary intake and the risk of getting a disease. Observational studies can not prove that a food caused a disease, only that those who consumed the food were more or less likely to get the disease. There are many limitations to these studies and their assumptions have occasionally been proven false in controlled trials, which are higher quality studies. Yet, despite their weaknesses, well-designed observational studies are an integral part of nutrition science. They provide important clues, especially when coupled with plausible biological explanations.

Bottom Line: Virtually all human studies on the connection between milk and cancer are observational in nature. They can not prove that dairy products cause a disease, only that consuming dairy is associated with it.

Colorectal Cancer

Colorectal cancer is cancer of the colon or rectum, the lowest parts of the digestive tract. It is one of the most common types of cancer in the world. Although the evidence is mixed, most studies indicate that eating dairy products may reduce the risk of colorectal cancer. Some components of milk may possibly protect against colorectal cancer, including:

  • Calcium.
  • Vitamin D.
  • Lactic acid bacteria, found in fermented dairy products like yogurt.

Bottom Line: Most studies suggest that consuming dairy products is linked to reduced risk of colorectal cancer.

Prostate Cancer

The prostate gland is located just below the bladder in men. Its main function is to produce prostate fluid, which is a part of semen.

In Europe and North America, prostate cancer is the most common type of cancer in men. Most large studies indicate that high dairy consumption may increase the risk of prostate cancer. One Icelandic study indicates that high milk consumption during early life may increase the risk of advanced prostate cancer later in life. Milk is a complex fluid containing a huge variety of bioactive compounds. Some of them may protect against cancer, while others may have adverse effects.

These include:

  • Calcium: One study has linked calcium from milk and supplements with an increased risk of prostate cancer, while some studies strongly suggest it has no effects.
  • Insulin-like growth factor 1 (IGF-1): IGF-1 has been linked with an increased risk of prostate cancer. However, this may be a consequence of cancer rather than a cause.
  • Estrogen hormones: Some researchers are concerned that the reproductive hormones in milk from pregnant cows may stimulate prostate cancer growth.

Bottom Line: The majority of studies suggest that high dairy consumption may increase the risk of prostate cancer. This may be due to several bioactive compounds found in milk.

Stomach Cancer

Stomach cancer, also known as gastric cancer, is the fourth most common cancer in the world. Many major studies have found no clear association between dairy intake and stomach cancer. Possible protective milk components may include conjugated linoleic acid (CLA) and certain probiotic bacteria in fermented milk products. On the other hand, insulin-like growth factor 1 (IGF-1) may promote stomach cancer. In many cases, what cows feed on often affects the nutritional quality and health properties of their milk. For example, milk from pasture-raised cows that feed on bracken ferns contains ptaquiloside, a toxic plant compound that may increase the risk of stomach cancer.

Bottom Line: In general, there is no clear evidence linking the consumption of dairy products with stomach cancer.

Breast Cancer

Breast cancer is the most common form of cancer in women. Overall, the evidence indicates that dairy products have no effects on breast cancer. In fact, some studies indicate that dairy products, excluding milk, may have protective effects.

Bottom Line: There is no consistent evidence about dairy products affecting breast cancer. Some types of dairy may have protective effects.

How Much Milk Can You Safely Drink?

Since dairy may actually raise the risk of prostate cancer, it is sensible to avoid consuming excessive amounts.

The current dietary guidelines for dairy recommend 2–3 servings or cups per day. The purpose of these recommendations is to ensure adequate intake of minerals, such as calcium and potassium. They do not account for a possible cancer risk. So far, official recommendations have not put a maximum limit on dairy consumption. There is simply not enough information for evidence-based recommendations. However, it may be a good idea to limit your intake to no more than two servings of dairy products per day, or an equivalent of two glasses of milk.

Bottom Line: Avoid excessive consumption of dairy products. Limit your intake to two servings of dairy products per day, or about two glasses of milk.

Take Home Message

Studies indicate that high dairy consumption increases the risk of prostate cancer. Yet, at the same time, dairy products may reduce the risk of colorectal cancer. For other types of cancer, the results are more inconsistent but generally indicate no adverse effects. Keep in mind that most of the available evidence is based on observational studies, which provide suggestive evidence but not definite proof. However, it is better to be safe than sorry. Consume dairy in moderation and base your diet on a variety of fresh, whole foods.

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8 Health Foods That are Harmful if You Eat Too Much

There are many super healthy foods out there. However, it’s important to keep in mind that more is not always better. Some foods can be good for you in moderation, but seriously harmful in large amounts. Here are 8 incredibly healthy foods that can harm you if you eat too much of them.

1. Omega-3 and Fish Oils

Omega-3 fatty acids are essential for our health. They fight inflammation in the body, play an important role in brain development and reduce the risk of heart disease, to name a few. Since most diets are low in omega-3, supplements have been gaining popularity. The most common supplements include omega-3 capsules produced from fish, fish liver and algae. However, too much omega-3 may be harmful. The usual dose ranges from 1–6 grams per day, but taking as much as 13–14 grams per day may have blood-thinning effects in healthy individuals. This may be risk, especially for people who are prone to bleeding or are taking blood-thinning medications. Furthermore, taking high amounts of fish liver oil may result in excessive vitamin A intake, which may cause vitamin A toxicity. This is of particular concern for children and pregnant women.

Bottom Line: Omega-3 fatty acids are essential for good health. However, excess omega-3 may have blood-thinning effects. Fish oil is also very high in vitamin A, which can be dangerous in large amounts.

2. Tuna (Both Fresh and Canned)

Tuna is a fatty fish that is usually considered to be very healthy. It is a good source of omega-3 fatty acids and is very high in protein. However, tuna may also contain high levels of an environmental pollutant called methylmercury. At higher levels, methylmercury is a neurological toxin that may cause many adverse health effects. These include developmental delays in children, vision problems, lack of coordination and impaired hearing and speech. Large tuna fish contain the most mercury, since it builds up in their tissues over time. These big tunas are very likely to be served to you as premium fish steaks or used in sushi. Smaller tunas contain lower amounts of mercury, and are more likely to be canned. There are two main types of canned tuna, and their mercury content differs:

  • White tuna: Light in color and usually comes from albacore fish. White tuna contains 4–5 times the amount of mercury found in light tuna.
  • Light tuna: Light tuna contains much less mercury than white tuna. It is darker in color and usually doesn’t come from albacore fish.

The upper safety limit of methylmercury for humans is 0.1 micrograms per kilogram of body weight. This means that a 25 kg (55 lb) child could only eat one 75 g (2.6 oz) serving of canned, white tuna every 19 days. Any more than this would exceed the recommended upper limit. Pregnant women and children are advised to limit their intake of seafood containing mercury to no more than two times per week. There are several other types of fish that are also rich in omega-3 fatty acids, but less likely to be contaminated with mercury. These include salmon, mackerel, sardines and trout.

Bottom Line: Tuna contains many important nutrients. However, it may also be contaminated with methylmercury due to pollution of the oceans.

3. Cinnamon

Cinnamon is a delicious, widely-used spice that may have some medicinal properties.

It is high in antioxidants and has been shown to fight inflammation and lower blood sugar levels. Eating cinnamon has also been linked to a reduced risk of heart disease, diabetes, cancer and neurodegenerative diseases. However, cinnamon contains high amounts of a compound called coumarin, which may be harmful in large doses. There are two main types of cinnamon, with different amounts of coumarin:

  • Cassia: Also known as regular cinnamon, Cassia cinnamon contains a relatively high amount of coumarin.
  • Ceylon: Known as the true cinnamon, Ceylon is the less common of the two. It is much lower in coumarin.

The tolerable daily intake of coumarin is 0.1 mg per kg of body weight. Consuming much more than that may cause liver toxicity and cancer. Based on the tolerable daily intake, it is not recommended to consume more than 0.5–2 grams of Cassia cinnamon each day. However, you can eat up to 5 grams (1 teaspoon) of Ceylon cinnamon per day. Eating more than that is fine occasionally, such as if a certain recipe calls for it. But large amounts should not be eaten too frequently.

Bottom Line: Cinnamon is antioxidant-rich and linked to several health benefits. Yet it also contains coumarin, which may be harmful in large doses. Of the two types of cinnamon, Ceylon cinnamon contains less coumarin.

4. Nutmeg

Nutmeg is a spice with a very unique taste. It is often used in Christmas foods like eggnog, cakes and puddings. Nutmeg contains a compound called myristicin, which is a psychoactive substance. In lower doses, nutmeg provides flavor to meals without affecting health. But in large doses, nutmeg may cause myristicin poisoning. The effects of myristicin poisoning include seizures, heart arrhythmias, nausea, dizziness, pain and hallucinations. Eating more than 10 grams of nutmeg in one sitting is not recommended. Higher doses than that have been shown to cause symptoms of toxicity.

Bottom Line: Nutmeg is used to flavor many foods. In low doses, it does not affect health. However, nutmeg contains myristicin, which can cause poisoning in large doses.

5. Coffee

Coffee is a wonderful beverage that is loaded with antioxidants and other active compounds.

It has been linked with numerous health benefits, including a reduced risk of liver diseases, type 2 diabetes and neurodegenerative diseases. The active ingredient in regular coffee is caffeine, with each cup containing an average of 80–120 mg. A daily intake of 400 mg is generally considered to be safe. However, consuming more than 500–600 mg per day can be excessive. This may overwhelm the nervous system, causing insomnia, nervousness, irritability, stomach cramps, heart palpitations and muscle tremors. The amount of caffeine needed to experience these side effects differs widely between individuals. Some can drink as much coffee as they want, while others experience symptoms with small amounts of caffeine.

Bottom Line: Coffee has been linked to many health benefits. However, too much caffeine may cause adverse effects in some people.

6. Liver

Organs are the most nutritious parts of animals, and liver is the most nutritious organ of all. It is very rich in many essential nutrients, such as iron, B12, vitamin A and copper. However, a 100 gram portion of beef liver contains more than six times the recommended dietary intake (RDI) of vitamin A, and 7 times the RDI of copper. Vitamin A is a fat soluble vitamin, meaning it is stored in our bodies. Therefore, an excess may cause symptoms of vitamin A toxicity. These symptoms may include vision problems, bone pain and an increased risk of fractures, nausea and vomiting. Eating too much copper may cause copper toxicity. This can lead to oxidative stress and neurodegenerative changes, and may increase the risk of Alzheimer’s disease. Even though liver is incredibly healthy and nutritious, it should not be consumed daily. Eating it once per week is enough.

Bottom Line: Liver contains many essential nutrients. However, it is very rich in vitamin A and copper, which may cause problems in excessive amounts.

7. Cruciferous Vegetables

Cruciferous vegetables are a family of greens that include broccoli, Brussels sprouts, kale, cabbage and collard greens.

These veggies have been linked with many health benefits, such as a reduced risk of cancer and heart disease. Cruciferous vegetables make up a large part of people’s daily vegetable intake. They have also become very popular as ingredients in various green smoothies and fresh vegetable juices. However, compounds in these vegetables called thiocyanates can interfere with the body’s ability to absorb iodine. This may contribute to a condition called hypothyroidism. Hypothyroidism is characterized by an underactive thyroid gland. Symptoms include an enlarged thyroid gland, weight gain, constipation, dry skin and reduced energy levels. Although cruciferous vegetables like broccoli are very healthy, adding high amounts to smoothies or green juices can contribute to a massive intake of these compounds. People who are sensitive to thyroid problems should avoid consuming these veggies in very large amounts.

Bottom Line: Cruciferous vegetables are healthy and nutritious. However, they contain thiocyanates, which can block iodine absorption. People with thyroid problems should not eat very large amounts of these veggies.

8. Brazil Nuts

Brazil nuts are among the best dietary sources of selenium. Selenium is an essential trace element, but can be toxic in high amounts. The recommended daily intake of selenium is 50–70 micrograms/day for adults. Additionally, the upper tolerance level for safe intake is about 300 micrograms/day for adults. One large Brazil nut may contain up to 95 micrograms of selenium. This is more than the recommended daily amount for adults, and more than three times the amount required by children. Eating only 4–5 Brazil nuts may leave an adult at the upper limit of safe selenium intake, so it is not recommended that you eat more than that. Symptoms of selenium toxicity include loss of hair and nails, digestive issues and memory difficulties.

Bottom Line: Brazil nuts contain selenium, which is an essential trace element. However, selenium is toxic in high amounts. Therefore, only a few Brazil nuts should be eaten each day.

Take Home Message

The foods on this list are all incredibly healthy. However, just because something is healthy in small amounts, it does not mean that large amounts are even healthier. When it comes to nutrition, more is not always better.

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Insulin and Insulin Resistance – The Ultimate Guide

Insulin is an important hormone that controls many processes in the body. However, problems with this hormone are at the heart of many modern health conditions. Sometimes our cells stop responding to insulin like they are supposed to. This condition is termed insulin resistance, and is incredibly common. In fact, a 2002 study showed that 32.2% of the US population may be insulin resistant. This number may rise to 70% in obese adult women and over 80% in some patient groups. About a third of obese children and teenagers may also have insulin resistance. These numbers are scary, but the good news is that insulin resistance can be dramatically improved with simple lifestyle measures. This article explains what insulin resistance is, why you should care and how you can overcome it.

Insulin and Insulin Resistance Explained

Insulin is a hormone secreted by an organ called the pancreas. Its main role is to regulate the amount of nutrients circulating in the bloodstream. Although insulin is mostly implicated in blood sugar management, it also affects fat and protein metabolism. When we eat a meal that contains carbohydrates, the amount of blood sugar in the bloodstream increases. This is sensed by the cells in the pancreas, which then release insulin into the blood. Then insulin travels around the bloodstream, telling the body’s cells that they should pick up sugar from the blood and bring it into the cells. This leads to reduced amounts of sugar in the blood, and puts it where it is intended to go, into the cells for use or storage. This is important, because high amounts of sugar in the blood can have toxic effects, causing severe harm and potentially leading to death if untreated. However, due to various reasons (discussed below), sometimes the cells stop responding to the insulin like they are supposed to. In other words, they become “resistant” to the insulin. When this happens, the pancreas start producing even more insulin to bring the blood sugar levels down. This leads to high insulin levels in the blood, termed hyperinsulinemia. This may continue to develop for a long time. The cells become increasingly more insulin resistant, and both insulin and blood sugar levels go up. Eventually, the pancreas may not be able to keep up anymore and the cells in the pancreas may become damaged. This leads to decreased insulin production, so now there are low amounts of insulin and cells that don’t respond to the little insulin that is available. This can lead to skyrocketing blood sugar levels. When blood sugar levels exceed a certain threshold, a diagnosis of type 2 diabetes is made. In fact, this is a simplified version of how type 2 diabetes develops. Insulin resistance is the main cause of this common disease that affects about 9% of people worldwide.

Resistance vs Sensitivity

Insulin resistance and insulin sensitivity are two sides of the same coin. If you are insulin resistant, then you have low insulin sensitivity. Conversely, if you are insulin sensitive then you have low insulin resistance. Being insulin resistant is a bad thing, while being insulin sensitive is good.

Bottom Line: Insulin resistance implies that the cells are not responding well to the hormone insulin. This causes higher insulin levels, higher blood sugar levels and may lead to type 2 diabetes and other health problems.

What Causes Insulin Resistance?

There are many potential causes and contributors to insulin resistance.

One of the main ones is believed to be increased amount of fats in the blood. Numerous studies show that high amounts of free fatty acids in the blood cause cells, such as muscle cells, to stop responding properly to insulin. This may be partly caused by fats and fatty acid metabolites building up inside muscle cells, termed intramyocellular fat. This disrupts the signalling pathways needed for insulin to work. The main cause of elevated free fatty acids is eating too many calories and carrying excess body fat. In fact, overeating, weight gain and obesity are all strongly associated with insulin resistance. Having increased visceral fat, the dangerous belly fat that builds up around the organs, seems to be very important. This type of fat may release lots of free fatty acids into the blood, and can even release inflammatory hormones that drive insulin resistance. However, normal weight or thin people can also be insulin resistant, it is just much more common among those who are overweight. There are several other potential causes of insulin resistance:

  • Fructose: A high intake of fructose (from added sugar, not fruit) has been linked to insulin resistance in both rats and humans.
  • Inflammation: Increased oxidative stress and inflammation in the body may lead to insulin resistance.
  • Inactivity: Physical activity increases insulin sensitivity, and being inactive causes insulin resistance.
  • Omega-3: Eating omega-3 fatty acids can in many cases reduce insulin resistance. They can also lower blood triglycerides, which are often high in insulin resistant people.
  • Gut microbiota: There is evidence that a disruption in the bacterial environment in the gut can cause inflammation that exacerbates insulin resistance and other metabolic problems.

There are also various genetic and social factors, and blacks, Hispanics and Asians are at particularly high risk. This list is not definitive. There are many other factors that may affect insulin resistance/sensitivity.

Bottom Line: The main causes of insulin resistance may be overeating and increased body fat, especially in the belly area. Other factors include high sugar intake, inflammation, inactivity and genetics.

How to Know if You Are Insulin Resistant

There are several ways that your doctor can determine if you are insulin resistant. For example, having high fasting insulin levels is a good sign that you have insulin resistance. A test called HOMA-IR estimates insulin resistance based on your blood sugar and insulin levels, and is fairly accurate. There are also ways to measure blood sugar control more directly, such as an oral glucose tolerance test, where you are given a dose of glucose and then your blood sugar levels are measured for a few hours. If you are overweight or obese, especially with large amounts of fat around the belly area, then chances are very high that you are insulin resistant. There is also a skin condition called acanthosis nigrans, involving dark spots on the skin that can indicate insulin resistance. Having low HDL (“good” cholesterol) levels and high blood triglycerides are two other markers that are strongly associated with insulin resistance.

Bottom Line: Having high insulin levels and high blood sugar levels are key symptoms of insulin resistance. Other symptoms include lots of belly fat, high blood triglycerides and low HDL levels

Insulin Resistance, Metabolic Syndrome and Type 2 Diabetes

Insulin resistance is a hallmark of two very common conditions, metabolic syndrome and type 2 diabetes.

The metabolic syndrome is a group of risk factors associated with type 2 diabetes, heart disease and other problems. The symptoms are high blood triglycerides, low HDL levels, elevated blood pressure, central obesity (belly fat) and elevated blood pressure. Sometimes this condition is referred to as the “insulin resistance syndrome” Insulin resistance is also a major driver of type 2 diabetes. The high blood sugar levels are caused by the cells not responding to insulin anymore. Over time, the insulin-producing cells in the pancreas may stop functioning, leading to insulin deficiency as well. By stopping the development of insulin resistance, it may be possible to prevent most cases of metabolic syndrome and type 2 diabetes.

Bottom Line: Insulin resistance is at the heart of metabolic syndrome and type 2 diabetes, which are currently among the biggest health problems in the world.

Insulin Resistance is Linked to Heart Disease and All Sorts of Other Health Problems

Insulin resistance is also strongly associated with heart disease, which is the world’s biggest killer. In fact, people who are insulin resistant or have metabolic syndrome have up to a 93% greater risk of heart disease. There are many other diseases linked to insulin resistance. This includes non-alcoholic fatty liver disease, polycystic ovarian syndrome (PCOS), Alzheimer’s disease and cancer.

Bottom Line: Insulin resistance may cause a variety of diseases, including heart disease, non-alcoholic fatty liver disease, polycystic ovarian syndrome, Alzheimer’s disease and cancer.

Ways to Reduce Insulin Resistance (Improve Insulin Sensitivity)

The good thing about insulin resistance, is that it is very easy to influence it. In fact, changing your lifestyle is able to completely reverse insulin resistance in many cases. Here are several evidence-based ways to reduce insulin resistance:

  • Exercise: This may be the single easiest way to improve insulin sensitivity. The effect is almost immediate.
  • Lose belly fat: Try to lose some fat, especially the deep “visceral” fat from your liver and belly. This article lists several evidence-based tips on how to lose belly fat.
  • Stop Smoking: Tobacco smoking can cause insulin resistance, so quitting should help
  • Sugar: Try to reduce your intake of added sugars, especially from sugar-sweetened beverages.
  • Eat healthy: Eat a diet based mostly on whole, unprocessed foods. Include nuts and fatty fish.
  • Supplements: Taking a supplement called berberine can be effective to enhance insulin sensitivity and reduce blood sugar. Magnesium supplements may be helpful as well.
  • Sleep: There is some evidence that poor sleep causes insulin resistance, so improving sleep quality should help.
  • Stress: If excessive, try to manage your stress levels. Meditation has been shown to be helpful.
  • Donate blood: High levels of iron in the blood are linked to insulin resistance. For men and postmenopausal women, donating blood may improve insulin sensitivity.
  • Intermittent fasting: Following an eating pattern called intermittent fasting can improve insulin sensitivity.

Most of the items on the list also happen to be the same things we generally associate with good health, protection against disease and a long life. All this being said, keep in mind that nothing in this article is intended as medical advice. Insulin resistance is linked to various serious health problems, and I recommend that you speak to your doctor about your options. There are also various medical treatments that can work.

Bottom Line: Insulin resistance may be reduced or even completely reversed with simple lifestyle measures. These include exercise, eating healthy, losing belly fat and taking care of your sleep and stress levels.

Low-Carb Diets and Insulin Resistance

Another thing worth highlighting is low-carb diets. Diets that restrict carbohydrates can have incredibly powerful benefits against metabolic syndrome and type 2 diabetes, and this is partly mediated by reduced insulin resistance. However, when carb intake is very low, such as on a ketogenic diet, the body may induce an insulin resistant state in order to spare blood sugar for the brain. This is termed “physiological” insulin resistance (as opposed to “pathological”) and is not a bad thing.

Bottom Line: Low-carb diets reduce the harmful insulin resistance linked to metabolic disease. However, very low-carb ketogenic diets may induce a harmless type of insulin resistance that spares blood sugar for the brain.

Take Home Message

Insulin resistance may be one of the key drivers of many (if not most) of today’s chronic diseases, which are collectively killing millions of people every year. The good news is that it can be significantly improved with simple lifestyle measures, such as losing fat, eating healthy food and exercising. Preventing insulin resistance may be among the single most powerful things you can do to live a longer, healthier and happier life.

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A1 vs A2 Milk – Does it Matter?

The health effects of milk may depend on the breed of cow it came from. Currently, A2 milk is being marketed as a healthier choice than regular milk. It is claimed to have several health benefits, and to be easier to digest for people who are lactose intolerant. However, not all scientists agree that A2 milk is better for health. This article takes an objective look at the science behind A1 and A2 milk.

What Do A1 and A2 Mean?

Casein is the largest group of proteins in milk, making up about 80% of the total protein content. There are several types of casein in milk, and beta-casein is the second most common. Beta-casein exists in at least 13 different forms. The two most common forms of beta-casein are:

  • A1 beta-casein: Milk from breeds of cows that originated in northern Europe is generally high in A1 beta-casein. A1 milk comes from breeds like the Holstein, Friesian, Ayrshire and British Shorthorn.
  • A2 beta-casein: Milk that is high in A2 beta-casein is mainly found in breeds that originated in the Channel Islands and Southern France. This includes breeds like the Guernsey, Jersey, Charolais and Limousin.

Regular milk contains both A1 and A2 beta-casein, but A2 milk contains only A2 beta-casein. Some studies indicate that A1 beta-casein may be harmful, and that A2 beta-casein is a safer choice. This is the reason for the “A1 vs A2” debate.


A2 milk is produced and marketed by the A2 Milk Company, and contains no A1 beta-casein.

Bottom Line: A1 and A2 milk contain different types of a protein called beta-casein. Some studies indicate that A2 milk may be the healthier of the two.


Beta-casomorphin-7 (BCM-7) is the reason why regular milk is believed to be less healthy than A2 milk. BCM-7 is an opioid peptide that is released during the digestion of A1 beta-casein. A few research groups have suggested that BCM-7 may be harmful. While BCM-7 may affect the digestive system, it is not yet clear to what extent BCM-7 is absorbed intact into the blood. Studies have not found BCM-7 in the blood of healthy adults after drinking cow’s milk, but a few studies indicate that BCM-7 may be present in infants. BCM-7 has been extensively studied, but its health relevance still remains unclear. Below is a review of the scientific evidence linking A1 milk and BCM-7 with type 1 diabetes, heart disease, infant death, autism and digestive problems.

Bottom Line: Regular milk contains A1 beta-casein, which is partly broken down to beta-casomorphin-7 (BCM-7) in the stomach. BCM-7 has been linked with several adverse health effects.

Risk of Type 1 Diabetes

Type 1 diabetes is typically diagnosed in children, and is characterized by a lack of insulin in the body. Several studies indicate that drinking A1 milk during childhood may increase the risk of type 1 diabetes. However, these studies are observational in nature. They cannot prove that A1 beta-casein caused type 1 diabetes, only that those who got more of it were at a higher risk of getting the disease. Animal studies have provided conflicting results. Some have found no difference between A1 and A2 beta-casein. Others have shown A1 beta-casein to have either protective or adverse effects on type 1 diabetes. So far, no clinical trials in humans have investigated the effect of A1 beta-casein on type 1 diabetes.

Bottom Line: Several observational studies have found a link between A1 milk consumption during childhood and increased risk of type 1 diabetes. However, the evidence is mixed and more research is needed.

Risk of Heart Disease

Two observational studies have linked the consumption of A1 milk with an increased risk of heart disease.

This is supported by one experiment in rabbits. It showed that consuming A1 beta-casein promoted fat buildup in injured blood vessels. This buildup was much lower when the rabbits consumed A2 beta-casein. Fat accumulation may potentially clog blood vessels and cause heart disease. However, the human relevance of the results has been debated. So far, two human trials have investigated the effects of A1 milk on heart disease risk factors. One of them included 15 men and women who were at a high risk of heart disease. The study had a crossover design, meaning that all participants received A1 and A2 beta-casein at different periods during the study. The study didn’t find any significant adverse effects on risk factors for heart disease. Compared with A2 beta-casein, the A1 type had similar effects on blood vessel function, blood pressure, blood fats and inflammatory markers. Another study found no significant differences in the effects of A1 and A2 casein on blood cholesterol.

Bottom Line: There is no strong evidence that A1 milk increases the risk of heart disease. However, the long-term effects have not been studied.

Sudden Infant Death Syndrome

Sudden infant death syndrome (SIDS) is the most common cause of death in infants less than one year of age. SIDS is defined as the unexpected death of an infant, without an apparent cause. Some researchers have speculated that BCM-7 may be involved in some cases of SIDS. One study found high levels of BCM-7 in the blood of infants who temporarily stopped breathing during sleep. This condition, known as sleep apnea, is linked to an increased risk of SIDS. These results indicate that some children may be sensitive to the A1 beta-casein found in cow’s milk. However, further studies are needed before any firm conclusions can be reached.

Bottom Line: There is limited evidence that A1 milk may increase the risk of sudden death in infants. More research is needed.

Risk of Autism

Autism is a mental condition characterized by poor social interaction and repetitive behavior.

In theory, peptides like BCM-7 might play a role in the development of autism. However, studies do not support all of the proposed mechanisms. One study of infants found higher levels of BCM-7 in those who were fed cow’s milk, compared to those who were breastfed. However, levels of BCM-7 dropped quickly in some of the infants, whereas they remained high in others. For those who retained these high levels, BCM-7 was strongly associated with an impaired ability to plan and perform actions. Another study indicated that drinking cow’s milk may worsen behavioral symptoms in autistic children. On the other hand, some studies found no effects on behavior. So far, no human trials have specifically investigated the effects of A1 and A2 milk on symptoms of autism.

Bottom Line: There is no conclusive evidence about the effects of A1 milk on autism. However, the issue is complicated and needs to be studied further.

Digestive Health

Lactose intolerance is defined as the inability to fully digest the sugar (lactose) found in milk. This is a common cause of bloating, gas and diarrhea. The amount of lactose found in A1 and A2 milk is the same. However, some people feel that A2 milk causes less bloating than A1 milk. Supporting this, studies indicate that milk components other than lactose may cause digestive discomfort. Scientists have suggested that certain milk proteins may be responsible for some people’s milk intolerance. One trial in 41 men and women showed that A1 milk may cause softer stools than A2 milk in some individuals. Additionally, studies in rodents indicate that A1 beta-casein may significantly increase inflammation in the digestive system.

Bottom Line: There is growing evidence that A1 beta-casein may affect digestive function. However, further clinical trials are needed to confirm these results.

Take Home Message

The A1/A2 debate is still up in the air. A few studies indicate that A1 beta-casein may have adverse effects in certain individuals. However, the evidence is still too weak for any strong conclusions to be made. That being said, if you feel like you tolerate A2 milk better than A1 milk, then you should definitely stick to it.

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