MANY people have been making the case that Americans have grown fat because they eat too much starch and sugar, and not enough meat, fat and eggs. Recently, the Dietary Guidelines Advisory Committee lifted recommendations that consumption of dietary cholesterol should be restricted, citing research that dietary cholesterol does not have a major effect on blood cholesterol levels. The predictable headlines followed: "Back to Eggs and Bacon?"

But, alas, bacon and egg yolks are not health foods.

Although people have been told for decades to eat less meat and fat, Americans actually consumed 67 percent more added fat, 39 percent more sugar, and 41 percent more meat in 2000 than they had in 1950 and 24.5 percent more calories than they had in 1970, according to the Agriculture Department. Not surprisingly, we are fatter and unhealthier.

The debate is not as simple as low-fat versus low-carb. Research shows that animal protein may significantly increase the risk of premature mortality from all causes, among them cardiovascular disease, cancer and Type 2 diabetes. Heavy consumption of saturated fat and trans fats may double the risk of developing Alzheimer’s disease.

A study published last March found a 75 percent increase in premature deaths from all causes, and a 400 percent increase in deaths from cancer and Type 2 diabetes, among heavy consumers of animal protein under the age of 65 — those who got 20 percent or more of their calories from animal protein.

Low-carb, high-animal-protein diets promote heart disease via mechanisms other than just their effects on cholesterol levels. Arterial blockages may be caused by animal-protein-induced elevations in free fatty acids and insulin levels and decreased production of endothelial progenitor cells (which help keep arteries clean). Egg yolks and red meat appear to significantly increase the risk of coronary heart disease and cancer due to increased production of trimethylamine N-oxide, or TMAO, a metabolite of meat and egg yolks linked to the clogging of arteries. (Egg whites have neither cholesterol nor TMAO.)

Animal protein increases IGF-1, an insulin-like growth hormone, and chronic inflammation, an underlying factor in many chronic diseases. Also, red meat is high in Neu5Gc, a tumor-forming sugar that is linked to chronic inflammation and an increased risk of cancer. A plant-based diet may prolong life by blocking the mTOR protein, which is linked to aging. When fat calories were carefully controlled, patients lost 67 percent more body fat than when carbohydrates were controlled. An optimal diet for preventing disease is a whole-foods, plant-based diet that is naturally low in animal protein, harmful fats and refined carbohydrates. What that means in practice is little or no red meat; mostly vegetables, fruits, whole grains, legumes and soy products in their natural forms; very few simple and refined carbohydrates such as sugar and white flour; and sufficient "good fats" such as fish oil or flax oil, seeds and nuts. A healthful diet should be low in "bad fats," meaning trans fats, saturated fats and hydrogenated fats. Finally, we need more quality and less quantity.

My colleagues and I at the nonprofit Preventive Medicine Research Institute and the University of California, San Francisco, have conducted clinical research proving the many benefits of a whole-foods, plant-based diet on reversing chronic diseases, not just on reducing risk factors such as cholesterol. Our interventions also included stress management techniques, moderate exercise like walking and social support.

We showed in randomized, controlled trials that these diet and lifestyle changes can reverse the progression of even severe coronary heart disease. Episodes of chest pain decreased by 91 percent after only a few weeks. After five years there were 2.5 times fewer cardiac events. Blood flow to the heart improved by over 300 percent. 

Other physicians, including Dr. Kim A. Williams, the president of the American College of Cardiology, are also finding that these diet and lifestyle changes can reduce the need for a lifetime of medications and transform people’s lives. These changes may also slow, stop or even reverse the progression of early-stage prostate cancer, judging from results in a randomized controlled trial.

These changes may also alter your genes, turning on genes that keep you healthy, and turning off genes that promote disease. They may even lengthen telomeres, the ends of our chromosomes that control aging.The more people adhered to these recommendations (including reducing the amount of fat and cholesterol they consumed), the more improvement we measured — at any age. But for reversing disease, a whole-foods, plant-based diet seems to be necessary.

In addition, what’s good for you is good for our planet. Livestock production causes more disruption of the climate than all forms of transportation combined. And because it takes as much as 10 times more grain to produce the same amount of calories through livestock as through direct grain consumption, eating a plant-based diet could free up resources for the hungry.What you gain is so much more than what you give up.

Dean Ornish, clinical professor of medicine at the University of California, San Francisco and the founder of the Preventive Medicine Research Institute.

Post your thoughts below. Happy Eating!