Fewer Calories Consumed in Low-Fat Vegan vs. Keto Diet

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Fewer Calories Consumed in Low-Fat Vegan vs. Keto Diet

Many people with diabetes are trying to lose weight, for both personal and medical reasons. The benefits of weight loss for overweight or obese people with diabetes are well documented, showing that losing as little as 5% of your body weight can improve your insulin sensitivity and blood glucose control — something that can be helpful for people with both type 1 and type 2 diabetes.

But figuring out how to lose weight is often the tricky part. While the basics of weight loss are simple, in theory — burn more calories than you take in — in practice it’s usually not so simple. People get hungry, have cravings for certain foods, and can feel low-energy or cranky on a calorie-restricted diet. People can also get fatigued from having to exercise their willpower by avoiding “bad” foods or beverages, and find it difficult to stick to restrictions — especially in social situations.


So it’s worth considering the practical effects of following specific diets that don’t involve calorie restriction, but instead limit the intake of entire categories of food. A recent study looked at people’s calories intake on two different diets aimed at achieving weight loss, but in very different ways — a low-fat vegan diet, and a low-carbohydrate ketogenic (keto) diet. The results show that if weight loss is your goal, a low-fat vegan diet may be a better choice.

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More carbs but fewer calories in low-fat vegan diet

The study, published in the journal Nature Medicine, included 20 younger adults (the average age was 30) who were admitted as inpatients to the National Institutes of Health Clinical Center for four weeks. The average body-mass index (BMI, a measure of weight that takes height into account) of participants was 27.8, which falls in the “overweight” category. Participants were randomly assigned to follow one of two diets for two weeks, then to follow the other diet.

One diet was a low-fat vegan diet consisting of about 75% carbohydrates and 10% fat. The other was a low-carbohydrate, mostly animal-based ketogenic diet consisting of about 75% fat and 10% carbohydrates. Both diets were minimally processed and contained the same amount of non-starchy vegetables. Throughout the study period, participants were provided daily meals and a continuous supply of snacks (compatible with their assigned diet) and water. The total supply of food and beverages each day was estimated to be twice the number of calories each participant needed — so participants were essentially free to eat as many calories as they wanted.

Overall, participants consumed an average of 689 fewer calories each day on the low-fat vegan diet than on the low-carbohydrate ketogenic diet. During the second week of each two-week diet period, participants consumed an average of 544 calories fewer each day on the low-fat vegan diet — showing that the difference in caloric intake between the two diets shrank during the second week.

Still, consuming over 500 fewer calories on the low-fat vegan diet is a big difference. What’s more, participants didn’t express an overall preference for one diet over the other — rating foods in each diet as similarly pleasant and familiar. There were also no significant differences in reported hunger, fullness or satisfaction between the two diets.

Different benefits from different diets

The researchers noted that this wasn’t a weight-loss study, so their purpose wasn’t to figure out which diet led to more weight loss. Instead, it was to figure out whether people tended to consume more calories on one diet or the other, and to look at some other basic measurements.

One notable difference between the low-fat vegan diet and the low-carbohydrate ketogenic diet was participants’ insulin levels, which were much higher on the low-fat vegan diet — not surprising, considering the much greater carbohydrate intake. For people with diabetes who have insulin resistance, this level of carbohydrate intake could be problematic and lead to an increase in blood glucose levels, especially after meals.

But if you’re looking to lose weight and can effectively control your blood glucose levels on a low-fat vegan diet, this study shows that it may be worthy of your consideration. Of course, you may choose to make further modifications, such as reducing carbohydrates and increasing protein on this type of diet — something that this study didn’t look at.

Be sure to talk with your doctor before starting any special diet to make sure you can do so safely, without an increased risk of hypoglycemia (low blood glucose) — especially if you take insulin or other diabetes drugs that carry a risk of hypoglycemia.

Want to learn more about eating well with diabetes? Read “Improving Your Recipes: One Step at a Time,” “Top Tips for Healthier Eating” and “Cooking With Herbs and Spices.”

Quinn Phillips

Quinn Phillips

Quinn Phillips on social media

A freelance health writer and editor based in Wisconsin, Phillips has a degree from Harvard University. He is a former Editorial Assistant for Diabetes Self-Management and has years of experience covering diabetes and related health conditions. Phillips writes on a variety of topics, but is especially interested in the intersection of health and public policy.

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