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:

Why Did Doctors Keep Prescribing Cancer?

We’ve known about the role of estrogen in breast cancer going back to the 1800s, when surgical removal of the ovaries seemed to help in some cases. Ovaries were said to send out “mysterious” influences to the rest of the body, which were identified as estrogen in 1923. The medical profession jumped on this discovery and started injecting menopausal women by the thousands, and it was said that “[t]he ‘shot’ gives a ‘respectable’ hook on which to hang the visit to the doctor…” Soon, there were pills and patches, and medical journals like the Journal of the American Medical Association regaled doctors with ads I feature in my video How Did Doctors Not Know About the Risks of Hormone Therapy? on how they can “help the women to happiness by simply prescribing estrogen” and, “[w]hen women outlive their ovaries…,” there is Premarin.

As far back as the 1940s, concerns were raised that this practice might cause breast cancer, noting it would have been nice to figure this out before we started dosing women en masse. But breast cancer risk didn’t seem to matter as much, because heart disease was the number-one killer of women, reviews concluded, and because women taking hormones appeared to have lower heart attack rates, which would outweigh any additional breast cancer. However, women taking estrogen tended to be of a higher socioeconomic class, exercised more, and engaged in other healthy lifestyle changes like consuming more dietary fiber and getting their cholesterol checked. So, maybe that’s why women taking estrogen appeared to be protected from heart disease. Perhaps it had nothing to do with the drugs themselves. Despite the medical profession’s “enthusiasm for estrogen replacement therapy,” only a randomized clinical trial could really resolve this question. We would need to divide women into two groups, with half getting the hormones and half getting a placebo, and follow them out for a few years. There was no such study…until the 1990s, when the Women’s Health Initiative study was designed.

Wait a second. Why did it take the bulk of a century to decide to definitively study the safety of something prescribed to millions of women? Perhaps because there had never been a female director of the National Institutes of Health until then. “Just three weeks after being named NIH Director in 1991, [Bernadine Healy] went before Congress to announce, ‘We need a moon walk for women.’ That ‘moon walk’ took the form of the Women’s Health Initiative, the most definitive, far-reaching clinical trial of women’s health ever undertaken in the United States.”

The bombshell landed in summer 2002. There was so much more invasive breast cancer in the hormone users that they were forced to stop the study prematurely. What about heart disease? Wasn’t that supposed to balance things out? The women didn’t just have more breast cancer—they had more heart attacks, more strokes, and more blood clots to their lungs.

The news that women treated with hormone replacement therapy “experienced higher rates of breast cancer, cardiovascular disease, and overall harm has rocked women and physicians across the country.” Estrogen started out as the most prescribed drug in America before the study, but, after, the number of prescriptions dropped immediately and, within a year, so did the incidence of breast cancer in the United States.

The most important question about this story is why were we all so surprised? There had been “decades of repeated warnings” about the risks of cancer. In fact, the reason breast cancer patients had so much trouble suing the pharmaceutical company was that “the drugs have contained warning labels for decades.” And, with that disclosure, surely any reasonable physician would have included it in their risk and benefit discussions with their patients, right? It’s like the warning labels on packs of cigarettes. If you get lung cancer now, you should have known better. And, so, if you were on hormone replacement therapy and got breast cancer, don’t blame the drug company. They warned you about the risks, right there in the fine print.

Why didn’t more doctors warn their patients? Even after the study came out, millions of prescriptions continued to be dispensed. That’s a lot of cancer in our patients we caused, wrote one doctor. “How long will it take us to discard the financial gains, to admit that we are harming many of our patients, and to start changing our prescription habits?”

“Why did this practice continue in the face of mounting evidence of harm?” Well, it is a multibillion-dollar industry. “Despite an overwhelming amount of evidence to the contrary, many physicians still believe that estrogenic hormones have overall health benefits,” a “non-evidence-based perception [that] may be the result of decades of carefully orchestrated corporate influence on medical literature.” Indeed, “[d]ozens of ghostwritten reviews and commentaries published in medical journals and supplements were used to promote unproven benefits and downplay harms of menopausal hormone therapy…” PR companies were paid to write the articles that were then passed off as having been written by some expert.

What now? “Gynecologists must switch allegiance from eminence-based to evidence-based medicine.” In other words, they must consider what the science says and not just what some so-called expert says. It’s been said that the “current culture of gynecology encourages the dissemination of health advice based on advertising rather than science.”

“Women were placed in the way of harm by their physicians, who acted as unsuspecting patsies for the pharmaceutical companies.” If we really wanted to prevent heart attacks in women, simple lifestyle behaviors can eliminate more than 90 percent of heart attack risk. So, instead of being Big Pharma’s pawns, “recommending a healthful diet, increased exercise, and smoking cessation would truly benefit women’s health.”


The whole Premarin debacle speaks to the importance of putting purported therapies to the test (see, for example, Do Vitamin D Supplements Help with Diabetes, Weight Loss, and Blood Pressure?), as well as to the power of Big Pharma (Eliminating Conflicts of Interest in Medical Research), medical community collusion (American Medical Association Complicity with Big Tobacco), and my most series on mammograms.

What about Plant-Based Bioidentical Hormones and Soy Phytoestrogens for Menopause Hot Flashes? Check out the videos to find out.

In general, patients (and doctors) tend to wildly overestimate the efficacy of pills and procedures. See Why Prevention Is Worth a Ton of Cure and The Actual Benefit of Diet vs. Drugs.

Medical care, in general, may be the third leading cause of death in the United States. See How Doctors Responded to Being Named a Leading Killer.

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:

Dishonest Doctors

One of the critical questions to ask whenever reading a medical journal article is, “Who funded the study?” In most journals, researchers are required to identify their sources of funding, so what’s the problem? Well, researchers can obscure the true origin of financial support: They can hide it, disguise it, or even launder the money through a front group. A case in point is a study downplaying the risks of lung cancer that was funded in part by the Foundation for Lung Cancer: Early Detection, Prevention, and Treatment. That doesn’t sound so bad until you realize it was underwritten by millions of dollars from a tobacco company. There’s no obligation to “disclose a funding source’s source of funding,” which allows “companies to evade financial disclosure requirements” and makes it harder to “follow the money trail.”

As I discuss in my video Disclosing Conflicts of Interest in Medical Research, why does the funding source matter? Every single one of eight reviews covering over a thousand studies found that research funded by industry is more likely to make conclusions that are favorable to industry. For example, why do some review articles on the health effects of secondhand smoke reach different conclusions than others? The only factor found was whether an author was affiliated with the tobacco industry. “This is a disturbing finding. It suggests that, far from conflict of interest being unimportant in the objective and pure world of science…it is the main factor determining the result of studies.”

Not that we’d even know, because 77 percent of authors failed to disclose the sources of funding. And that’s another problem: The responsibility to disclose funding sources is left entirely up to the authors. So, how many researchers divulge the truth? Evidently, a law was passed in Denmark requiring physicians to register any time they worked with industry, which allowed researchers to cross-reference the studies physicians published to see how honest they were. Forty-eight percent of the time, the conflicts of interest were not disclosed, “reinforc[ing] the perception that physicians simply don’t take conflict of interest seriously” (or at least Danish physicians don’t).

What about the United States? Historically, there had been “no means of confirmation or verification” when an American doctor said they had no conflict of interest. Then in 2007, hip and knee replacement companies were forced to pay hundreds of millions of dollars in fines for giving orthopedic surgeons illegal kickbacks. “[M]any orthopedic surgeons in [the] country made decisions predicated on how much money they could make—choosing which device to implant by going to the highest bidder….[W]e expect doctors to make decisions based on what is in the best interests of their patients,” said the Department of Justice’s U.S. Attorney of the District of New Jersey, “not the best interests of their bank accounts.” Part of the settlement was that the companies would have to make public all the payments they made to physicians. The release of those records offered a rare opportunity to see if physicians were telling the truth on disclosure forms. And, lo and behold, more than half of payments were not disclosed, totalling millions of dollars.

That was for surgeons and medical device companies. What about doctors and drug companies? The same thing happened: Drug companies were forced to disclose who they were paying off. In looking at the publications of the doctors who got the most money—at least $100,000—the study found that they were worse than the surgeons. In 69 percent of the cases, they failed to disclose their industry ties. The problem is that we just assume researchers are going to be honest and tell the truth, but these “findings suggest that the accuracy and completeness of [conflict-of-interest] disclosures cannot be assumed.” So, even when a paper says no conflict of interest, who knows if it’s really true.

A long-time editor-in-chief of the New England Journal of Medicine wrote a scathing piece on drug companies and doctors who failed to disclose hundreds of thousands of dollars from drug companies like GlaxoSmithKline, which has been fined literally billions of dollars for activities such as bribing and suppressing data. When GSK got results that were “commercially unacceptable,” the company just buried them. Billions of dollars in fines get assessed, but for drug companies, that may just be the cost of doing business. “As reprehensible as many [drug] industry practices are…much of the medical profession is even more culpable.” We can expect drug companies to prioritize the bottom line, but maybe we should expect more from the healing profession.


What else might your doctor not be telling you? See:

Good examples of conflicts of interest include:

Instead of just disclosing conflicts of interest, how about getting rid of them? That’s the subject of my video Eliminating Conflicts of Interest in Medical Research.

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: