Scientists compared 5 low-carb diets and found 1 made losing weight and keeping it off easier

• Low-carb diets are popular ways to lose weight.
• Scientists studied whether the quality of low-carb diets made a difference to long-term weight loss.
• A high-quality, low-carb diet emphasizing plant-based foods was linked to slower weight gain.

Eating a healthy low-carb diet that emphasizes high-quality plant-based proteins, fats, and carbs such as whole grains has been associated with long-term weight loss in a study.

In contrast, less healthy low-carb diets high in animal proteins, fats, and less nutrient-dense carbs such as refined starches had the opposite effect and were associated with faster weight gain.

The study, published on Wednesday in JAMA Network Open, sheds new light on low-carb diets, which have long been popular methods for weight loss, from Atkins to keto.

However, long-term weight loss is notoriously difficult to achieve, and experts have previously told Business Insider the best diet for losing fat and keeping it off is the one that a person can stick to — low-carb or otherwise.

The authors highlighted that extremely low-carb diets can be unsustainable, which is partly why keto was named the worst diet for healthy eating in 2022 in US News and World Report's annual ranking.

A high-quality, low-carb diet could make long-term weight loss easier

The authors of the study set out to understand if low-carb diets could help people lose weight long-term, and whether the quality of foods made a difference.

The researchers used data from existing studies collected between 1986 and 2018, on 123,332 participants based in the US. The participants, who were age 45 on average, mostly women and mostly white, shared information about their diet and weight when they first joined their respective studies and then biennially.

To chart changes in weight among the participants, the team looked at the data in four-year intervals.

The authors categorized the participants according to whether they followed what they described as:

• A total low-carbohydrate diet: that was overall low in carbs

• An animal-based LCD: emphasizing animal proteins and fats

• A vegetable-based LCD: emphasizing plant-based fats and proteins

• A healthy LCD: emphasizing fewer refined carbs, more plant proteins, and healthy fats

• Or an unhealthy LCD: emphasizing less healthy sources of carbs, unhealthy fats, and animal proteins.

Coauthor Binkai Liu, a research assistant in the department of nutrition at Harvard T.H. Chan School of Public Health, told Business Insider that the diets analyzed contained around 40% carbs, setting them apart from keto, which can allow as little as 5%.

People who ate low-carb diets that focused on high-quality proteins, fats, and carbs from healthy plant-based foods, including whole grains, were more likely to put on weight slower in the long term, while lower-quality low-carb diets had the opposite effect.

Liu told CNN those on unhealthy LCDs gained on average about 5.1 pounds over four years, while those on healthy low-carb diets lost 4.9 lbs on average.

The authors said the findings show how important the quality of a person's low-carb diet is for maintaining weight loss long-term.

Diets packed with whole foods are best

"The key takeaway here is that not all low-carbohydrate diets are created equal when it comes to managing weight in the long-term," senior author Qi Sun, associate professor in the Department of Nutrition at Harvard T.H. Chan School of Public Health, said in a statement. "Our findings could shake up the way we think about popular low-carbohydrate diets and suggest that public health initiatives should continue to promote dietary patterns that emphasize healthful foods like whole grains, fruits, vegetables, and low-fat dairy products."

The authors acknowledged their study had limitations, including relying on participants accurately reporting changes to their weight and diet. It also didn't measure the participants' body composition, including belly fat levels, meaning the team couldn't find out if the LCDs were linked to changes in lean body mass and fat levels. Future research should aim to replicate their results in more diverse populations and try to explain the links, they said.

Dr. David Katz, a preventive medicine specialist who was not involved in the study, told CNN the observational study wasn't designed to establish cause and effect, but said the links are "hard to explain away."

Katz told CNN the bottom line of the study is that simply following a low-carb diet in general doesn't aid lasting weight loss, whereas a plant-based and high-quality, low-carb diet was associated with sustained weight loss.