Research says replacing meat with plant-based foods, even processed, is best for weight loss

Replacing animal products with plant-based foods, even ultra-processed options like soy milk and veggie burgers, can significantly aid weight loss, new research shows. Nutrition Insight speaks to the study’s lead researcher about processed plant foods, additives, oils, and the health impact of diets rich in these foods.

Without calorie restrictions, participants in a low-fat, plant-based diet lost an average of 13 pounds (5.9 kg) in 16 weeks, reveals the study, published in Nutrition & Metabolism. The findings challenge the idea that processed plant-based foods are unhealthy and that they can be part of a weight-loss strategy.

Hana Kahleova, MD, PhD, director of clinical research for the Physicians Committee for Responsible Medicine, tells us the research emphasizes that the key factor was removing animal products, which are high in saturated fat and cholesterol while increasing fiber-rich plant foods.

Does eating processed plant foods help health as much as whole plant foods?
Kahleova: The key to improving health is replacing animal products with plant-based foods, regardless of their level of processing. Animal products like meat, eggs, and dairy are generally high in saturated fat, contain cholesterol, and have no fiber, while plant-based foods, even processed ones, are cholesterol-free, mostly low in fat, and contain varying amounts of fiber. Whole plant foods — fruits, vegetables, grains, and beans — tend to be the lowest in fat and highest in fiber and have provided the most benefits for weight loss in our study. Hana Kahleova, lead author of the study.

Would a high-fat vegan diet, like one with nuts and avocados, have the same results?
Kahleova: Even plant-based foods that are higher in fat, like avocados and nuts, contain fiber, which is beneficial for weight loss. But 1 g of fat, regardless of its source, has nine calories, while 1 g of carbohydrate, including from potatoes, bread, or beans, has only four calories, so a vegan diet that limits fat is most beneficial for weight loss. 

Do additives and oils in processed plant foods cause any health risks?
Kahleova: A new study shows that substituting butter with plant-based oils may help prevent premature death from heart disease and cancer. Other research has shown the benefits of replacing animal-based sources of fat with plant-based sources of fat to reduce heart disease risk. At the same time, our findings showed that limiting fat intake, including oil, is beneficial for weight loss and overall health.

The fat, cholesterol, additives, and naturally occurring compounds in animal products present the greatest risk. For example, dairy products contain hormones linked to breast and prostate cancers; the cancer-causing compound PhIP is formed when meat is cooked at high temperatures; animal products are higher in compounds called advanced glycation end products that are linked to inflammation; and processed meats like bacon and hot dogs have been linked to colorectal cancer and heart disease.Whole plant foods tend to be the lowest in fat and highest in fiber and have provided the most benefits for weight loss in our study.

Does this diet help people who are not overweight or just those trying to lose weight?
Kahleova: Yes, participants who have followed a low-fat vegan diet in our other clinical research studies have experienced health benefits, including weight loss, improvements in type 2 diabetes and heart health, reduced rheumatoid arthritis pain, and reduced insulin needs for those with type 1 diabetes, among other health improvements.

Did the study look at long-term health effects or just short-term weight loss?
Kahleova: This study was 16 weeks long and did not look at the long-term health effects, but our previous research has shown the long-term benefits of weight loss. In the study, 64 women who were moderately or severely overweight followed a low-fat vegan diet for 14 weeks and lost 13 pounds, on average, without calorie counting or exercise. A year later, they’d maintained an 11-pound weight loss. After two years, they were still below their original weight.