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:

Why Drinking Diet Soda Makes You Crave Sugar

Recommendations on limiting sugar consumption vary around the world, with guidelines ranging from “[l]imit sweet desserts to one every other day” to “[k]eep sugar consumption to 4 or less occasions per day.” In the United States, the American Heart Association is leading the charge, “proposing dramatic reductions in the consumption of soft drinks and other sweetened products” and recommending fewer than about 5 percent of calories a day from added sugars, which may not even allow for a single can of soda.

Why is the American Heart Association so concerned about sugar? “Overconsumption of added sugars has long been associated with an increased risk of cardiovascular disease,” meaning heart disease and strokes. We used to think added sugars were just a marker for an unhealthy diet. At fast-food restaurants, for example, people may be more likely to order a cheeseburger with their super-sized soda than a salad. However, the new thinking is that the added sugars in processed foods and drinks may be independent risk factors in and of themselves. Indeed, worse than just empty calories, they may be actively disease-promoting calories, which I discuss in my video Does Diet Soda Increase Stroke Risk as Much as Regular Soda?.

At 1:14 in my video, you can see a chart of how much added sugar the American public is consuming. The data show that only about 1 percent meet the American Heart Association recommendation to keep added sugar intake down to 5 or 6 percent of daily caloric intake. Most people are up around 15 percent, which is where cardiovascular disease risk starts to take off. There is a doubling of risk at about 25 percent of calories and a quadrupling of risk for those getting one-third of their daily caloric intake from added sugar.

Two hundred years ago, we ate an estimated 7 pounds of sugar annually. Today, we may consume dozens of pounds of sugar a year. We’re hardwired to like sweet foods because we evolved surrounded by fruit, not Froot Loops, but this adaptation is “terribly misused and abused” today, “hijacked” by the food industry for our pleasure and their profits. “Why are we consuming so much sugar despite knowing too much can harm us?” Yes, it may have an addictive quality and there’s the hardwiring, but the processed food industry isn’t helping. Seventy five percent of packaged foods and beverages in the United States contain added sweeteners, mostly coming from sugar-sweetened beverages like soda, which are thought responsible for more than a 100,000 deaths worldwide and millions of years of healthy life lost. Given this, can we just switch to diet sodas? By choosing diet drinks, can’t we get that sweet taste we crave without any of the downsides? Unfortunately, studies indicate that “[r]outine consumption of diet soft drinks is linked to increases in the same risks that many seek to avoid by using artificial sweeteners—namely type 2 diabetes, metabolic syndrome heart disease, and stroke.” At 3:15 in my video, you can see data showing the increased risks of cardiovascular disease associated with regular soft drinks and also diet soda. They aren’t that dissimilar.

“In other words, the belief that artificially sweetened diet beverages reduce long-term health risks is not supported by scientific evidence, and instead, scientific data indicate that diet soft drink consumption may contribute to the very health risks people have been seeking to avoid.” But, why? It makes sense that drinking all that sugar in a regular soft drink might increase stroke risk, due to the extra inflammation and triglycerides, but why does a can of diet soda appear to increase stroke risk the same amount? It’s possible that the caramel coloring in brown sodas like colas plays a role, but another possibility is that “artificial sweeteners may increase the desire for sugar-sweetened, energy-dense beverages/foods.”

The problem with artificial sweeteners “is that a disconnect ultimately develops between the amount of sweetness the brain tastes and how much glucose [blood sugar] ends up coming to the brain.” The brain feels cheated and “figures you have to eat more and more and more sweetness in order to get any calories out of it.” So, “[a]s a consequence, at the end of the day, your brain says, ‘OK, at some point I need some glucose [blood sugar] here.’ And then you eat an entire cake, because nobody can hold out in the end.”

If people are given Sprite, Sprite Zero (a zero-calorie soda), or unsweetened, carbonated, lemon-lime water, but aren’t told which drink they’re getting or what the study is about, when they’re later offered a choice of M&M’s, spring water, or sugar-free gum, who do you think picks the M&M’s? Those who drank the artificially sweetened soda were nearly three times more likely to take the candy than those who consumed either the sugar-sweetened or unsweetened drinks. So, it wasn’t a matter of sweet versus non-sweet or calories versus no-calories. There’s something about non-caloric sweeteners that somehow tricks the brain.

The researchers did another study in which everyone was given Oreos and were then asked how satisfied the cookies made them feel. Once again, those who drank the artificially sweetened Sprite Zero reported feeling less satisfied than those who drank the regular Sprite or the sparkling water. “These results are consistent with recent [brain imaging] studies demonstrating that regular consumption of [artificial sweeteners] can alter the neural pathways responsible for the hedonic [or pleasure] response to food.”

Indeed, “[t]he only way really to prevent this problem—to break the addiction—is to go completely cold turkey and go off all sweeteners—artificial as well as fructose [table sugar and high fructose corn syrup]. Eventually, the brain resets itself and you don’t crave it as much.”

We’ve always assumed the “[c]onsumption of both sugar and artificial sweeteners may be changing our palates or taste preferences over time, increasing our desire for sweet foods. Unfortunately, the data on this [were] lacking”…until now. Twenty people agreed to cut out all added sugars and artificial sweeteners for two weeks. Afterwards, 95 percent “found that sweet foods and drinks tasted sweeter or too sweet” and “said moving forward they would use less or even no sugar.” What’s more, most stopped craving sugar within the first week—after only six days. This suggests a two-week sugar challenge, or even a one-week challenge, may “help to reset taste preferences and make consuming less or no sugar easier.” Perhaps we should be recommending it to our patients. “Eating fewer processed foods and choosing more real, whole, and plant-based foods make it easy to consume less sugar.”


Speaking of stroke, did you see my Chocolate and Stroke Risk video?

For more on added sugars, see:

You may also be interested in my videos on artificial and low-calorie sweeteners:

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: