What Happens When Pregnant Women Eat More Animal Protein

Are high-protein diets during pregnancy healthful or harmful? That question was answered about 40 years ago in the infamous Harlem Trial of 1976: a “randomized controlled trial of nutritional supplementation pregnancy, in a poor black urban population in the United States.” The study, which I discuss in my video The Effect of Animal Protein on Stress Hormones, Testosterone, and Pregnancy, “was begun when protein was commonly assumed to be deficient in the diet of the poor.” Had researchers actually analyzed their diets before they started, they would have realized that this wasn’t true, but why let facts get in the way of assumptions? So, the researchers split poor black pregnant women into three groups, each receiving one of the following treatments: (1) an extra 40 grams of animal protein a day, which is essentially a couple cans of Ensure, (2) an extra 6 grams of animal protein, or (3) no extra protein. Then they sat back and watched what happened. The high-protein group suffered “an excess of very early premature births and associated neonatal [infant] deaths, and there was significant growth retardation” in the babies who survived. More protein meant more prematurity, more deaths, and more growth retardation, which you can see reflected in the chart at 1:00 in my video.

What’s more, animal protein intake during pregnancy has been associated with children becoming overweight later in life and getting high blood pressure. The “offspring of mothers who reported eating more meat and fish had higher systolic blood pressure” in adulthood. This was part of another failed dietary intervention trial in which mothers were advised to eat a pound of meat a day. The increased weight gain and high blood pressure may be due to the obesity-causing chemical pollutants in the meat supply, as I’ve discussed in my video Animal Protein, Pregnancy, and Childhood Obesity, or the animal protein-induced rise in the growth hormone IGF-1. Or, it could be due to a steroid stress hormone called cortisol.

As you can see in the chart at 2:01 in my video, a single meal high in animal protein can nearly double the level of the stress hormone in the blood within a half hour of consumption, much more than a meal closer to the recommended level of protein. When subjects are given a meal of crab, tuna fish, and cottage cheese, the stress hormone level shoots up. If they’re instead given some barley soup and a vegetable stir-fry on rice, the stress hormone level goes down after the meal, as you can see at 2:27 in my video. Imagine eating meat-fish-dairy meals day after day. Doing so “may chronically stimulate” our stress response axis “and increase the release of vasoactive hormones” that could increase our blood pressure. And, all that extra cortisol release has been linked to increased risk for elevated blood levels of insulin, triglycerides, and cholesterol.

When men on a high-protein diet, “such as meat, fish, poultry, egg white,” were switched to a high-carb diet of bread, vegetables, fruit, and sugary junk, their cortisol levels dropped about a quarter within 10 days. At the same time, their testosterone levels shot up by about the same amount, as you can see at 3:09 in my video. High-protein diets suppress testosterone. That is why, if men eating plant-based diets begin to eat meat every day, their testosterone levels go down and some estrogens actually go up, and that’s why bodybuilders can get such low testosterone levels. It’s not the steroids they’re taking. If you look at natural bodybuilders who don’t use steroids, there is a 75 percent drop in testosterone levels in the months leading up to a competition. Testosterone levels were cut by more than half, which is enough to drop a guy into an abnormally low range, as you can see at 3:47 in my video. It’s ironic that they’re eating protein to look manly on the outside, but it can make them less and less manly on the inside. And, from an obesity standpoint, in general, a drop in testosterone levels may increase the risk of gaining weight and body fat. What does cortisol have to do with weight?

There’s actually a disease caused by having too much cortisol, called Cushing’s syndrome, which can increase abdominal obesity. Even in normal women, though, chronic stress and chronic high cortisol levels can contribute to obesity. What’s more, if they’re pregnant, high-meat and low-carb diets may increase cortisol levels in the moms, which can lead to inappropriate fetal exposure to cortisol, which, in turn, can affect the developing fetus, resetting her or his whole stress response thermostat and leading to higher cortisol levels in later adult life. This can have serious, life-long health consequences. Every maternal daily portion of meat and fish was associated with 5 percent higher cortisol levels in their children as much as 30 years later, though green vegetable consumption was found to be protective. Higher meat consumption, such as three servings a day compared to one or two, was associated with significantly higher cortisol levels, but eating greens every day appeared to blunt some of that excess stress response, as you can see at 5:12 in my video.

As well, the adult children of mothers who ate a lot of meat during pregnancy don’t only have higher stress hormone levels, they also appear to react more negatively to whatever life throws at them. Researchers put them through the Trier Test, which involves public speaking in front of a panel of judges, following by a live math exercise. You can see in my video at 5:36 a chart comparing the stress hormone responses in those whose moms ate less than two servings of meat per day, about two servings a day, or about two to three servings a day. Note that before the test started, the cortisol levels of the two groups eating less meat started out about the same, but their exaggerated cortisol response was laid bare when exposed to a stressful situation. The real-world effects of this are that after that sort of test, when people are given their own private snack buffet with fruits and veggies versus fatty, sugary, comfort foods like chocolate cake, guess who may eat less of the fruits and veggies? Those who have high chronic stress levels. “Cortisol has been implicated as a factor in motivating food intake” even when we aren’t really hungry.

It’s no surprise then that a woman’s animal protein intake during pregnancy may lead to larger weight gain for her children later in life—and maybe even for her grandchildren. “Remarkably, recent evidence suggests that the long-term consequences of adverse conditions during early development may not be limited to one generation, but may lead to poor health in the generations to follow, even if these individuals develop in normal conditions themselves.” Indeed, the diet of a pregnant mother may affect the development and disease risk of her children and even her grandchildren. Ultimately, these findings may shed light on our rapidly expanding epidemics of diabetes, obesity, and heart disease.


Whoa, there was a lot to unpack! Rather than break it up, since so much of it was tied together, as you could see, I compiled everything into this one, heftier piece. You may want to read this a second time and watch the video to absorb it all.

For more on how a woman’s diet during pregnancy can affect her children, see Maternal Diet May Affect Stress Responses in Children and Animal Protein, Pregnancy, and Childhood Obesity.

Protein is such a misunderstood nutrient. For more information, check out:

In health,
Michael Greger, M.D.

PS: If you haven’t yet, you can subscribe to my free videos here and watch my live presentations:

How Not to Die from Cancer

After Dr. Dean Ornish conquered our number-one killer, heart disease, he moved on to killer number-two. What happens if cancer is put on a plant-based diet? Ornish and colleagues found that the progression of early-stage prostate cancer could be reversed with a plant-based diet and other healthy lifestyle behaviors.

If the blood of those eating the Standard American Diet is dripped onto cancer cells growing in a petri dish, cancer growth is cut down about 9 percent. And if they’ve followed a plant-based diet for a year? Their blood can slash cancer growth by 70 percent. So the blood circulating thgouhout the bodies of those eating plant-based diets had nearly eight times the stopping power when it came to suppressing cancer cell growth.

That was for cell growth of prostate cancer, the leading cancer-killer specific to men. In younger women, breast cancer is the top cancer-killer. Researchers wanted to repeat the study with women using breast cancer cells, but they didn’t want to wait a whole year to get the results. Women are dying now. So they figured they’d see what a plant-based diet could do after just two weeks against three different types of human breast cancer.

As you can see in my video How Not to Die from Cancer, the study showed cancer growth started out at 100 percent, but then dropped after the subjects ate a plant-based diet for 14 days. A layer of breast cancer cells was laid down in a petri dish, and then blood from women eating the Standard American Diet was dripped on it. As you can see in the video, even the blood of women eating pretty poor diets had some ability to break down cancer. After just two weeks of eating healthfully, though, blood was drawn from those same women—so they effectively acted as their own controls—and was dripped on a new carpet of breast cancer cells. You can see for yourself that only a few individual cancer cells remained. Their bodies cleaned up. After only 14 days on a plant-based diet, their bloodstream became that much more hostile to cancer.

Slowing down the growth of cancer cells is nice, but getting rid of them all together is even better. This is what’s called apoptosis, programmed cell death. After eating healthfully, the women’s own bodies were able to somehow reprogram the cancer cells, forcing them into early retirement.

In my video, you can see what’s called TUNEL imaging, which allows researchers to measure DNA fragmentation, or cell death. With this technology, dying cancer cells appear as little white spots. From the start of the study, you can see one small white speck in the upper left of the image, showing that the blood of an average woman on a typical American diet can knock off a few breast cancer cells. After 14 days of healthy, plant-based living, however, her blood turned that one small white speck into a multitude of white spots. It’s as if she’s an entirely different woman inside! The same blood now coursing through these women’s bodies gained the power to significantly slow down and even stop breast cancer cell growth after just two weeks of eating a plant-based diet.

What kind of blood do we want in our body? What kind of immune system? Do we want blood that just rolls over when new cancer cells pop up, or do we want blood circulating to every nook and cranny of our body with the power to slow down and stop them?

The dramatic strengthening of cancer defenses shown in the study was after 14 days of a plant-based diet—and exercise.The researchers had the women walking 30 to 60 minutes a day. Given there were two factors, how do we know what role the diet played? Researchers decided to put it to the test.

In my video, you can see a chart that first shows how blood taken from those who ate a plant-based diet and had a routine of mild exercise, such as walking every day, over an average of 14 years, exhibited significant cancer cell clearance. The researchers then compared the substantial cancer-stopping power of plant eaters to that of an average sedentary American, which you can see is basically nonexistent.

The researchers also analyzed a third group. Instead of 14 years on a plant-based diet, they had 14 years on a Standard American Diet, but they also had 14 years of daily, strenuous, hour-long exercise, like calisthenics. They wanted to know if you exercised hard enough and long enough could you rival some strolling plant eaters.

The answer? There’s no question that exercise helped, but literally 5,000 hours in the gym was no match for a plant-based diet.

Once again using TUNEL imaging to analyze cancer cell death, the researchers found that even if you are a couch potato eating fried potatoes, your body isn’t totally defenseless. Your bloodstream can kill off some cancer cells, which you can see in my video as a couple white spots in the first image of that series. If you exercise for 5,000 hours, you can kill many more cancer cells, evidenced by the many more white specks appearing throughout that image. But nothing appears to kick more cancer tush than a plant-based diet, as that image is filled with white spots indicating cancer cells killed off.

Why is this the case? We think it’s because animal proteins, such as meat, egg white, and dairy protein, increase the level of insulin-like growth factor-1 (IGF-1), a cancer-promoting growth hormone involved in the “acquisition or progress of malignant tumors.”

In my video, you can see the results of a study that nailed IGF-1 as the villain. Just as in the previous studies, subjects went on a plant-based diet and cancer-cell growth dropped, while cancer-cell death shot up. This experiment, however, had a kicker: It added back to the cancer just the amount of IGF-1 that had been banished from your body as a result of eating and living healthier. In doing so, it effectively erased the “diet and exercise” effect. It’s as if the subjects had never started eating healthfully at all, with the cancer-cell growth rates and death rates returning to the same levels as before the plant-based diet intervention.

The reason one of the largest prospective studies on diet and cancer found “the incidence of all cancers combined was lower among vegetarians than among meat eaters” may be because they eat less animal protein, and thereby end up with less IGF-1, which means less cancer growth.

How much less cancer growth? A study found that middle-aged men and women with high protein intakes had a 75 percent increase in overall mortality and a fourfold increase in the risk of dying specifically from cancer. Does the protein source matter? Yes. It was specifically animal protein, which makes sense, given their higher IGF-1 levels.

The academic institution where the study was done sent out a press release with a memorable opening line: “That chicken wing you’re eating could be as deadly as a cigarette.” It went on to explain that “eating a diet rich in animal proteins during middle age makes you four times more likely to die from cancer…—a mortality risk factor comparable to smoking.”

What was the response to the revelation that diets high in meat, eggs, and dairy could be as harmful to health as smoking? One nutrition scientist replied it was “‘potentially even dangerous’ to compare the effects of smoking with the effect of meat and cheese,” but why? Because, they argued, a smoker might think “‘why bother quitting smoking if my cheese and ham sandwich is just as bad for me?’”

This reminds me of a famous Philip Morris cigarette ad that tried to downplay the risks of second-hand smoke. The ad included a chart with “everyday activities” and “reported relative risk,” in an attempt to say second-hand smoke wasn’t all that bad. The chart showed that while it increases the risk of lung cancer by 19 percent, drinking one or two glasses of milk every day may be three times as bad with a 62 percent higher risk of lung cancer. Lung cancer risk could be doubled if you frequently cook with oil, and heart disease risk tripled if you eat non-vegetarian or multiplied six-fold by eating lots of meat and dairy. Philip Morris’s conclusion? “Let’s keep a sense of perspective.” The “risk of lung cancer from second-hand tobacco smoke [was put] well below the risk reported by other studies for many everyday items and activities.”

That’s like saying, “Don’t worry about getting stabbed, because getting shot is so much worse.” Two risks don’t make a right.

Of course, you’ll note Philip Morris stopped throwing dairy under the bus once it purchased Kraft Foods.


The first time someone visits NutritionFacts.org can be overwhelming. With videos on more than 2,000 health topics, where do you even begin? Imagine stumbling onto the site not knowing what to expect and the new video-of-the-day is about how a particular spice can be effective in treating a particular form of arthritis. It would be easy to miss the forest for the trees, which is precisely why I created a series of overview videos that are essentially taken straight from my live, hour-long 2016 presentation How Not to Die: Preventing, Arresting, and Reversing Our Top 15 Killers.

The other videos in this overview series are:

Inspired to learn more about the role diet may play in preventing and treating cancer? Check out these other popular videos on the topic:

I’ve also produced an entire series on mammograms. You can find all of those videos here.

In health,
Michael Greger, M.D.

PS: If you haven’t yet, you can subscribe to my free videos here and watch my live, year-in-review presentations:

How Can Animal Protein Intake Increase Childhood Obesity Risk?

If pregnant crickets are exposed to a predatory wolf spider, their babies will hatch, exhibiting increased antipredator behavior and, as a consequence, improved survival from wolf spider attack. The mother cricket appears to be able to forewarn her babies about the threat when they are still inside her, so they would be pre-adapted to their external environment. This even happens in plants. If you grow two genetically identical plants—one in the sun, one in the shade—the sun-grown plant will produce seeds that grow better in the sun, and the shaded plant will produce seeds that grow better in the shade—even though they’re genetically identical.

What’s happening is called epigenetics, external factors changing gene expression.

Vole pups born in the winter come out growing thicker coats. Vole mothers are able to communicate the season to their babies in utero and tell them to put a coat on even before they’re born. We’re no different. You know how some people have different temperature tolerances, resulting in “battles of the bedroom”? Do you turn the AC on or off? Open the windows? It’s not just genetics. Whether we’re born in the tropics or in a cold environment determines how many active sweat glands we have in our skin.

What does this have to do with diet? As I discuss in my video Animal Protein, Pregnancy, and Childhood Obesity, can what a pregnant woman eats—or doesn’t eat—permanently alter the biology of her children in terms of what genes are turned on or off throughout life?

What happened to the children born during the 1944 – 1945 Dutch famine imposed by the Nazis? They had higher rates of obesity 50 years later. The baby’s DNA gene expression was reprogrammed before birth to expect to be born into a world of famine and conserve calories at all cost. But when the war ended, this propensity to store fat became a disadvantage. What pregnant women eat and don’t eat doesn’t just help determine the birth weight of the child, but the future adult weight of the child.

For example, maternal protein intake during pregnancy may play a role in the obesity epidemic—but not just protein in general. “Protein from animal sources, primarily meat products, consumed during pregnancy may increase risk of overweight in offspring…” Originally, researchers thought it might be the IGF-1, a growth hormone boosted by animal product consumption, that may increase the production of fatty tissue, but weight gain was tied more to meat intake than dairy. Every daily portion of meat intake during the third trimester of pregnancy resulted in about an extra 1 percent of body fat mass in their children by their 16th birthday, potentially increasing their risk of becoming obese later in life, independent of how many calories they ate or how much they exercised.  But no such link was found with cow’s milk intake, which would presumably boost IGF-1 levels just as high.

Given that, perhaps instead of IGF-1, it’s the obesogens in meat, chemicals that stimulate the growth of fatty tissue. “[E]merging evidence demonstrates that environmental factors can predispose exposed individuals to gain weight, irrespective of diet and exercise.” After all, even our infants are fatter, and we can’t blame that on diet and exercise. Animals are fatter, too, and not just our pampered pets—even rats in laboratories and subways are bigger. “The likelihood of 24 animal populations from eight different species all showing a positive trend in weight over the past few decades by chance was estimated at about 1 in 10 million” so it appears something else is going on—something like obesogenic chemicals.

One such candidate is polycyclic aromatic hydrocarbons (PAHs), which are found in cigarette smoke, vehicle exhaust, and grilled meat. A nationwide study of thousands found that the more children were exposed to PAHs, the fatter they tended to be. The researchers could measure the level of these chemicals right out of their urine. Exposure can start in the womb. Indeed, prenatal exposure to these chemicals may cause increased fat mass gained during childhood and a higher risk of childhood obesity.

If these pollutants sound familiar, I’ve covered them before in relation to increasing breast cancer risk in the Long Island Breast Cancer Study Project. So, perhaps they aren’t just obesogens, but carcinogens, as well, which may help explain the 47 percent increase in breast cancer risk among older women in relation to a lifetime average of grilled and smoked foods.

If we look at one of the most common of these toxins, smokers get about half from food and half from cigarettes. For nonsmokers, however, 99 percent comes from diet. The highest levels of PAHs are found in meat, with pork apparently worse than beef. Even dark green leafies like kale can get contaminated by pollutants in the air, though, so don’t forage for dandelion greens next to the highway and make sure to wash your greens under running water.

These are fat-soluble pollutants, so they need lots of fat to be absorbed. It’s possible that even heavily contaminated plant-based sources may be safer, unless you pour lots of oil on your food, in which case the toxins would presumably become as readily absorbed as the toxins in meat.

The good news is they don’t build up in our body. As I show in my video, if we expose people to barbecued chicken, they get a big spike in these chemicals—up to a hundred-fold increase—but our body can get rid of them within about 20 hours. The problem, of course, is that people who eat these kinds of foods every day could be constantly exposing themselves, which may not only affect their health and their children’s health, but maybe even their grandchildren’s health.

Being pregnant during the Dutch famine of the mid-1940s didn’t just lead to an increase in diseases among their kids, but even apparently their grandkids. What a pregnant woman eats now may affect future generations. “The issue of generation-spanning effects of poor conditions during [pregnancy]…may shed light on the epidemic of diabetes, obesity and cardiovascular disease,” which is associated with the transition towards Western lifestyles.


Epigenetics is the science of altering the expression of our genes. No matter our family history, some genes can be effectively turned on and off by the lifestyle choices we make. See, for example:

For more on “obesogenic” chemicals, see:

I previously touched on PAHs in Meat Fumes: Dietary Secondhand Smoke.

In health,
Michael Greger, M.D.

PS: If you haven’t yet, you can subscribe to my free videos here and watch my live, year-in-review presentations: