The most effective diet for weight loss may also be the most healthful.

Why are vegetarian diets so effective in preventing and treating diabetes? Maybe it is because of the weight loss. As I discuss in my video The Best Diet for Weight Loss and Disease Prevention, those eating more plant-based tend to be significantly slimmer. That isn’t based on looking at a cross-section of the population either. You can perform an interventional trial and put it to the test in a randomized, controlled community-based trial of a whole food, plant-based diet.

“The key difference between this trial [of plant-based nutrition] and other approaches to weight loss was that participants were informed to eat the WFPB [whole food, plant-based] diet ad libitum and to focus efforts on diet, rather than increasing exercise.” Ad libitum means they could eat as much as they want; there was no calorie counting or portion control. They just ate. It was about improving the quality of the food rather than restricting the quantity of food. In the study, the researchers had participants focus just on a diet rather than exercising more exercise because they wanted to isolate the effects of eating more healthfully.

So, what happened? At the start of the study, the participants were, on average, obese at nearly 210 pounds (95 kg) with an average height of about 5’5” (165 cm). Three months into the trial, they were down about 18 pounds (8 kg)—without portion restrictions and eating all the healthy foods they wanted. At six months in, they were closer to 26 pounds (12 kg) lighter. You know how these weight-loss trials usually go, though. However, this wasn’t an institutional study where the participants were locked up and fed. In this trial, no meals were provided. The researchers just informed them about the benefits of plant-based eating and encouraged them to eat that way on their own, with their own families, and in their own homes, in their own communities. What you typically see in these “free-living” studies is weight loss at six months, with the weight creeping back or even getting worse by the end of a year. But, in this study, the participants were able to maintain that weight loss all year, as you can see below and at 1:57 in my video.

What’s more, their cholesterol got better, too, but the claim to fame is that they “achieved greater weight loss at 6 and 12 months than any other trial that does not limit energy [caloric] intake or mandate regular exercise.” That’s worth repeating. A whole food, plant-based diet achieved the greatest weight loss ever recorded at 6 and 12 months compared to any other such intervention published in the medical literature. Now, obviously, with very low-calorie starvation diets, you can drop down to any weight. “However, medically supervised liquid ‘meal replacements’ are not intended for ongoing use”—obviously, they’re just short-term fixes—“and are associated with ‘high costs, high attrition rates, and a high probability of regaining 50% or more of lost weight in 1 to 2 years.’” In contrast, the whole point of whole food, plant-based nutrition is to maximize long-term health and longevity.

What about low-carb diets? “Studies on the effects of low-carbohydrate diets have shown higher rates of all-cause mortality”—meaning a shorter lifespan—“decreased peripheral flow-mediated dilation [artery function], worsening of coronary artery disease, and increased rates of constipation, headache, halitosis [bad breath], muscle cramps, general weakness, and rash.”

The point of weight loss is not to fit into a smaller casket. A whole food, plant-based diet is more effective than low-carb diets for weight loss and has the bonus of having all good side effects, such as decreasing the risk of diabetes beyond just weight loss.

“The lower risk of type 2 diabetes among vegetarians may be explained in part by improved weight status (i.e., lower BMI). However, the lower risk also may be explained by higher amounts of ingested dietary fiber and plant protein, the absence of meat- and egg-derived protein and heme iron, and a lower intake of saturated fat. Most studies report the lowest risk of type 2 diabetes among individuals who adhere to vegan diets. This may be explained by the fact that vegans, in contrast to ovo- and lacto-ovo-vegetarians, do not ingest eggs. Two separate meta-analyses linked egg consumption with a higher risk of type 2 diabetes.”

Maybe it’s eating lower on the food chain, thereby avoiding the highest levels of persistent organic pollutants, like dioxins, PCBs, and DDT in animal products. Those have been implicated as a diabetes risk factor. Or maybe it has to do with the gut microbiome. With all that fiber in a plant-based diet, it’s no surprise there would be fewer disease-causing bugs and more protective gut flora, which can lead to less inflammation throughout the body that “may be the key feature linking the vegan gut microbiota with protective health effects”—including the metabolic dysfunction you can see in type 2 diabetes.

The multiplicity of benefits from eating plant-based can help with compliance and family buy-in. “Whereas a household that includes people who do not have diabetes may be unlikely to enthusiastically follow a ‘diabetic diet,’ a low-fat plant-based approach is not disease-specific and has been shown to improve other chronic conditions. While the patient [with diabetes] will likely see improvement in A1C [blood sugar control], a spouse suffering from constipation or high blood pressure may also see improvements, as may children with weight issues,” if you make healthy eating a family affair.

This is just a taste of my New York Times best-selling book, How Not to Diet. (As with all of my books, all proceeds I received went to charity.) Watch the book trailer. You may also be interested in its companion, The How Not to Diet Cookbook.

Check out my hour-long Evidence-Based Weight Loss lecture for more.