Veganism and Weight Loss Study

Fall 2005 issue of Dr. Michael Greger's quarterly newsletter

C. The Atkins Diet: Dead Meat

My latest book, "Carbophobia: The Scary Truth Behind America's Low Carb Craze": published February 1st, 2005. The multibillion dollar Atkins corporation: files for bankruptcy August 1st.[10] Six months. Not bad (though I was hoping to topple them in four :). Seriously, though, all the I-told-them-so satisfaction is lost upon reflection of the thousands of families shattered by pork-rind and egg-yolk fueled heart attacks spawned by these high-fat frauds. Americans are now fattening at a rate never before seen, with a recent report showing rising obesity rates across 48 states. Right now two thirds of Americans are overweight. By 2008 the number is predicted to approach 75%.[11] And just when we thought we couldn't get any fatter comes the follow-up to the Framingham Heart Study published last week in the Annals of Internal Medicine, suggesting that over the long haul as many as 9 out of 10 men are likely to become overweight.[12] The answer, according to two new studies piling onto the mountain of evidence, is a plant-based diet.

First, a study of over 50,000 Swedish women around age 50. The vegetarians were, not surprisingly, significantly leaner than the meateaters and those who eliminated all saturated animal fat from their diet (meat and dairy and eggs)--the vegan group--was the leanest of all. The study suggests that by choosing to eat vegetarian, people can cut their risk of becoming overweight in half, and eating vegan seems to cut out two thirds of the risk. The researchers note that the results are also likely "generalizable to younger women and to men."[13] The study understandably prompted press reports like "Skip This One Food. You'll Weigh Less."[14] The title of the Washington Post report was less cryptic: "To Cut Fat, Eat Less Meat."[15]

The weakness of the Swedish study, though, is that it's a cross-sectional study based on comparing populations. Maybe the vegetarians are slimmer because they are just generally more health conscious and exercised more? (Although they also might tend not to smoke which might bias the results the other way.) How do we know if there's a cause and effect relationship between a plant-based diet and a healthier weight? What we need, frankly, is a study that controls for exercise--a randomized interventional study. You put half of people on one diet, half on another and see what happens. Enter: September 2005 American Journal of Medicine study "The effects of a low-fat, plant-based dietary intervention on body weight, metabolism, and insulin sensitivity."[16]

Researchers at Georgetown and the George Washington University School of Medicine took 64 overweight and obese postmenopausal women and randomized them to one of two diets. The control diet approximated the official National Institutes of Health "Therapeutic Lifestyle Changes" diet, which emphasizes plant foods but includes lean cuts of meat, low fat dairy, and up to almost a whole egg's worth of cholesterol every day. So they compared this "strict" American Heart Association diet the federal government prescribes to those who've already had a heart attack or are at exceptionally high risk of heart disease to a completely plant-based diet akin to the Ornish prescription of a diet centered on vegetables, fruits, grains, and legumes.

Now dietary intervention studies are tricky to put together. Sure, if you lock someone up in a metabolic ward and measure out calorie-controlled portions to the gram you could show that eating almost any diet can cause significant weight loss, but that's not how the real world works. Realizing this, researchers typically allow people to remain at home, but hand-deliver precooked meals three times a day for the study's duration. This of course makes researchers nervous because who knows if they're actually eating what you're giving them. And what else are they hoarding away in their kitchens? But of course even this tends to artificially exaggerate the benefits of the diets given the convenience of hand-delivered meals. To translate a study's findings into real life, what you need to do is put people on different diets out in the real world. Encourage them to maintain the diets under study, but make the participants prepare their own meals or eat out in restaurants. So that's exactly what these researchers did--sat down each diet group and told them how to eat, but then basically set them lose to try to make it work in their own lives. Obviously this is a conservative approach which would tend to underplay the actual effects of the experimental diet under study, but these researchers realized that for practical purposes, it doesn't matter if a diet works in a lab. The real question is does it work in your life.

With unlimited servings, no limits on calorie intake, no hunger, no exercise requirement, the plant-based diet group lost significantly more weight (over 50% more) than the diet currently recommended to reduce disease risk. "Reductions in body mass index and waist circumference were also significantly greater in the intervention group, compared with the control group." "In conclusion," the researcher wrote, "in a controlled trial, the consumption of a low-fat, vegan diet was associated with significant weight reduction, along with improvements in measures of glucose tolerance and insulin sensitivity."

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