New Study Finds a Low-Fat Plant-Based Diet Beats Keto for Weight Loss

There are a host of benefits to eating plant-based a diet, from lowering your risk of every major disease to helping to save the planet. But now there is also a growing body of evidence that a plant-based diet will help you lose weight and be healthy too, since plant-based foods are rich in nutrients, antioxidants, and fiber and low in saturated fat. Now there is a new study to add to this: That plant-based diets are more effective for long-term weight-loss than the keto diet. Published in the journal Nature Medicine, the study, “Effect of a plant-based, low-fat diet versus an animal-based, ketogenic diet" researched the difference between a plant-based, low-fat diet and an animal-based, low-carb diet, to see how each one impacted weight loss.

Conducted by researchers at the National Institute of Diabetes and Digestive and Kidney Diseases, the study tracked 20 adults without diabetes for four continuous weeks in the NIH Clinical Center’s Metabolic Clinical Research Unit, providing them with three meals and snacks daily and allowing the 11 men and 9 women to eat as much as they wanted. For two weeks, they either received the plant-based, low-fat diet or the animal-based, low-carb keto diet and then after 2 weeks, they swapped to the alternate diet for two weeks.

While both diets led to weight loss, the plant-based diet allowed the participants to eat more calories per day and see a "significant loss of body fat," which the keto diet did not share. The plant-based dieters were as satisfied and satiated as the keto dieters. So all in all, they ate more and lose more body fat than when they were put on the keto plan.

“High-fat foods have been thought to result in excess calorie intake because they have many calories per bite. Alternatively, high-carb foods can cause large swings in blood glucose and insulin that may increase hunger and lead to overeating,” said NIDDK Senior Investigator Kevin Hall, Ph.D., the study’s lead author. “Our study was designed to determine whether high-carb or high-fat diets result in greater calorie intake.” Scientists then compared the results of these diets on calorie intake, hormone levels, weight, and other factors.

The researchers discovered that those on the low-fat plant-based diet consumed 550 to 700 fewer calories per day than when they ate the low-carb keto diet. Even though they were eating substantially fewer calories on the plant-based, low-fat diet, “study participants reported no differences in hunger, enjoyment of meals, or fullness between the two diets. Additionally, participants lost weight while on both of these dietary approaches, but only the plant-based, low-fat diet “led to a significant loss of body fat.” Future research would need to be conducted to see how these results stacked up over a longer period of time.

Ashley Shaw, a Registered Dietician for Preg Appetit!, who wasn’t associated with the research, broke down these findings for us, saying “currently, animal-based, high-fat diets are very popular for weight loss (i.e., keto, paleo) so this is positive news for those that are vegan or vegetarian, or just want a more plant-based lifestyle and also want to lose weight.” She did note, however, that while the plant-based diet led to greater body fat loss when compared to the animal-based keto diet, those on the plant-based diet had less stable blood sugar.

The study found there were several other benefits to eating plant-based, beyond weight loss. “Those consuming the plant-based diet could consume bigger portions because the foods are lower in calories per gram of food compared to the animal-based foods,” said Shaw, also noting that the plant-based diet contained much more fiber, which helps keep your appetite at bay. “This means that while those on this diet could eat more due to it being lower in calories, they were actually more likely to eat smaller portions,” she added. Eating a fiber-rich diet from fruits, veggies, grains, and beans, is also linked to a variety of positive health outcomes, including reduced risk of cardiovascular disease and cancer. (For more on fiber and its health benefits, check out this article.)

Beyond the latest study, there are many reasons experts believe going vegan can help promote weight loss. “A vegan diet is rich in heart-healthy fats and fiber, which together can be extremely beneficial for weight loss. Polyunsaturated fats actually help the body to metabolize fat for energy, whereas fiber makes you feel fuller faster and stay satisfied longer after a meal. That means smaller portions go a long way, and fewer calories are consumed,” said Shaw, further commenting that everyone is different, and for some, a higher fat diet is better for weight loss while others may need a higher carbohydrate or higher protein diet.

“What I like about this study is that it gives vegans/vegetarians an option since most plant-based food is higher in carbohydrates. This proves that keto is not the only option for weight loss, and may not even be that good of an option for those who consume animal-based foods,” Shaw continued. One important caveat, this study was designed in a tightly controlled laboratory setting: “A main factor of this study was that the foods consumed (whether plant- or animal-based) were minimally processed, something that is not as easy to achieve outside of a controlled environment,” she said, highlighting — on the plus side — that many who adhere to plant-based diets are more likely to eat foods that are minimally processed and more wholesome overall than those eating a standard American diet.

As Michele Sidorenkov, RDN cautions, there are certainly some high-carb, vegan diets that are unhealthy and can lead to weight gain. “I have heard of the term 'junk food vegan,’ which is someone who consumes a lot of processed, packaged vegan foods, like cookies and frozen snacks,” she said. “While a junk food vegan could fit into the category of eating high-carb vegan meals, they will not get the same weight loss or satiety as described in the research study...There are many ways someone could eat a high carbohydrate vegan diet, and they don't all result in weight loss.”

Despite the potential for unhealthy adaptation of a plant-based regime, as with any diet, Sidorenkov gives eating vegan the green light when it comes to slimming down. “Personally, I do feel like a vegan diet could be beneficial for someone who is trying to lose weight if the diet is sustainable, the person is feeling satisfied and not deprived, and they are including the proper amounts of plant-based proteins, carbohydrates, and healthy fats into every meal,” she explained.

For an example of what a nutritious day of plant-based eating could look like that follow a plant-based, low-fat diet, Shaw recommends the following:

Breakfast: Tropical smoothie with frozen mango and pineapple chunks, banana, baby spinach, hemp hearts, and nut milk of choice. (We love this refreshing mango and banana smoothie recipe.)

Lunch: Sprouted multigrain bread with nut butter and strawberry slices sprinkled with chia seeds

Dinner: Homemade burrito bowl with black beans and brown rice with Tex-Mex spices over a bed of lettuce topped with avocado, tomato, onion, jalapeño, and salsa.

Snacks: Peanut butter or almond butter with apple slices; hummus with carrot and celery sticks; guacamole and bell pepper strips.

Bottom Line: To lose weight and keep it off, switch to a plant-based diet high in whole foods like vegetables, fruit, whole grains, legumes, nuts and seeds.