Could Too Much Protein Explain the Link Between Meat & Heart Disease?

Everyone obsesses about getting enough protein, but now a new study tells us we are probably eating way too much. Like two and a half times more than is recommended, and it may just be the very thing that is leading to our increased risk of heart disease.

Researchers at Penn State College of Medicine looked at meat-eaters and vegan diets and found that the meat-eaters were intaking more than what is considered a healthy dose of sulfur amino acids, found in meat, poultry, fish and eggs. A better dosage was found in the diets of plant-based eaters who got their SAAs from veggies like onions, shallots, garlic, chives and leeks along with the usual lineup of cruciferous vegetables like broccoli, Brussel sprouts, kale, and cabbage.

So what is a healthy-eater to do? Stop worrying about getting enough protein, and start seeking plant-based sources of protein, especially from vegetables like broccoli, cauliflower, cabbage, and brussels sprouts, kale, spinach, asparagus, okra, sweet corn, and allium vegetables like onions, garlic, leeks, shallots and chives. Other plant sources include beans, and soybeans, which have the highest sulfur content.

The science is from a new study that tells us everything we need to know about amino acids, and perhaps more. How much protein you eat is part of the problem, but where that protein comes from is the main event. The study is brand new, even if its conclusions sound familiar, and echo the science we've been learning about plant-based diets and heart disease.

We know that red meat consumption is linked to a higher risk of heart disease, cancer, type 2 diabetes and premature death from all causes. But the question is why? The theories range from the effect that meat has on your microbiome to its artery-clogging fat content, or even the chemicals added to our food before it hits the table. One thing is agreed on: People who eat diets high in meat tend to be heavier and live shorter lives.

Now, a new study purports to hint at the reason this is true. The authors found that eating a diet high in animal protein increases the risk of developing a wide range of chronic diseases (again nothing new here) and then recommended eating plant-based protein diet to reduce these risks. The reason is the type of amino acids in the meat, which are called sulfur amino acids, or SAAs, in abundance, appear to increase the risk of heart disease. People who eat meat are getting two and a half times the recommended amount, or the Estimated Average Requirement (EAR), of SAAs in their diet, which may be contributing to risk factors for cardiometabolic diseases.

The study is the first to investigate what affect diets high in sulfur amino acids have on overall health. SAAs are found in many foods, but are highest in eggs, fish, red meat and chicken. When consumed in moderate or recommended amounts, sulfur amino acids play a crucial role in our bodies. They help metabolism, protect cells from damage, build proteins, regulate hormones and neurotransmitters, and help keep the liver functioning well.

But when there are too many SAAs, it can lead to heart disease, obesity, higher levels of insulin and a shorter lifespan. The authors recommend that the best way to regulate SAAs is to get them from plant-based sources, which offer lower doses of SAAs and are linked to healthier, longer lifespan and lower risks of disease.

Eating too many foods high in sulfur amino acids can have many negative health effects. They are linked to a higher risk of heart disease, stroke, diabetes, and non-alcohol fatty liver disease. And you're at even greater risk if you eat high levels of two particular types of sulfur amino acids, cysteine and methionine, both of which are found in high-protein foods. They are considered the most toxic amino acids, even though the body needs both.

The finding that low sulfur amino acid diets are typically more heavily reliant on plant-derived proteins suggests that sulfur amino acid reduction may be partly responsible for health benefits associated with a plant-based diet and offer a practical solution for reducing sulfur amino acid in the diet.

Sulfur-rich foods include "allium vegetables" which include garlic, onions, leeks scallions, chives, and shallots. It also is abundant in cruciferous vegetables like cabbage, brussels sprouts and broccoli, bok choy, collard greens, radishes, and watercress as well as kale.

According to the research, animal studies suggest diets restricted in sulfur amino acids are associated with many health benefits including increased longevity and reductions in age-related diseases.

Rats fed a diet low in amino acid, and with methionine as the sole sulfur amino acid source—meaning closer to the type found in plant-based diets—increased their maximum lifespan, and were healthier during their lifetime. This type of diet (where the SAAs come from plants) have been shown to delay aging in a number of animal and cell-based models.

Further, low SAA diets have been associated with reductions in body weight, adipose tissue (body fat) and oxidative stress (which leads to aging), higher metabolism, and positive changes in the levels of blood biomarkers, including insulin, glucose, leptin, and more. There is little data on the health benefits of low SAA diets in humans. The authors wrote that their goal was to investigate whether diets low in SAAs were associated with reduced risk for cardiometabolic diseases.

In general, it is recommended that adults only consume 15mg of sulfur amino acids per kilogram of body weight a day. But evidence shows that most adults have diets that exceed these recommendations by more than double. There are 9 essential amino acids that your body can't create on its own, and most of those come from food:

Your body needs 20 different amino acids to grow and function properly. Though all 20 of these are important for your health, only nine amino acids are classified as essential and those are histidine, isoleucine, leucine, lysine, methionine, phenylalanine, threonine, tryptophan and valine. The ones we get too much of are the SAAs that come from animal proteins, which are cysteine and methionine.

The researchers looked at a sample size of 11,576 adults as part of the National Health and Nutrition Examination Survey (NHANES III) over a period of six years. Researchers measured participants' diets, as well as cholesterol, insulin, and blood glucose levels, to see how they were affected by eating an abundance of SAAs.

The researchers found that the average subject they studied consumed 2.5 times the recommended levels of SAAs. After controlling for variables such as weight, race, and gender, they found that eating a diet high in SAAs, especially cysteine and methionine, was associated with higher cholesterol, insulin resistance and elevated blood glucose—all of which contribute to cardiometabolic diseases such as heart attacks, strokes, diabetes, and liver disease.

The health risks were not solely about overall protein consumption, but the amount and proportion of SAAs eaten. Because animal products contain higher levels of SAAs, the researchers recommend that a diet of plant-based proteins is the best way to reduce SAA consumption to healthier levels.

The authors' conclusion: Lower intake of sulfur amino acids may, in part, explain some of the observed health benefits of plant-based diets. Swapping animal-based protein sources for plant-based ones appears to be a good health move.

Nutrition is a major component of reducing overall risks of chronic disease and premature death. Sulfur amino acids are more prevalent in meat than vegetables, so switching to plant-based protein sources like whole grains, beans, lentils, nuts and seeds, and eating recommended daily intakes of sulfur amino acids, could make it less likely that you will develop heart disease or diabetes in future, the authors concluded.