Variations on the low-carb diet are popular ways to shed pounds, but a new study shows that the quality of food, not just the amount of carbs, fat and protein, makes a difference in weight loss.
The study, published on December 27, 2023, in JAMA network openedfollowed participants for decades to find out how five different types of low-carb diets affected weight.
“The key takeaway from our study is that not all low-carb diets are the same when it comes to long-term weight management – food quality is crucial,” said the study’s lead author, Binkai Liu, PhD, a research assistant at the nutrition department at the Harvard TH Chan School of Public Health in Boston.
Researchers found that diets low in carbohydrates, but high in high-quality protein, fat and a small portion of carbohydrates from healthy plant sources such as whole grains and beans, were linked to slower weight gain. “On the other hand, low-carb diets high in animal protein and fat or refined carbohydrates, such as those from red and processed meats, dairy products and sugar-sweetened beverages, can lead to faster weight gain,” says Dr. Liu. .
“This study is brilliant because it makes it clear that ‘low-carb’ is a crude term that is oversimplified. There are many ways to eat that can be called low-carb,” says Christopher Gardner, MD, a nutrition researcher and professor at Stanford Medicine in Palo Alto, California.
The findings from this large and long-term observational study suggest that the one approach clearly associated with the greatest benefit for weight maintenance is one that is healthy and plant-based, says Dr. Gardner, who was not involved in this research.
Study followed the eating patterns of 120,000 people for 30 to 40 years
Many studies have shown the benefits of cutting out carbohydrates for short-term weight loss. A meta-analysis of 25 studies published in April 2022 in Diabetes, obesity and metabolism found that low-carb diets were associated with “greater short-term weight loss than diets without carbohydrates.”
But this study aimed to address a gap in knowledge about how well low-carb eating works for long-term weight loss, and whether nutrient quality matters. Using data from the first and second Nurses’ Health Studies and the Health Professionals Follow-Up Study, researchers followed more than 120,000 healthy adults from 1986 to 2018.
Participants self-reported their diet and weight every four years through a survey that included more than 130 foods, of which nearly 70 foods contained animal protein.
The researchers rated the participants’ diets based on how well they adhered to five categories of low-carb diets, all of which consisted of 30 to 40 percent carbohydrates:
- A total low-carb diet simply focused on macronutrients that emphasized overall lower carbohydrate intake
- A low-carb animal diet, with an emphasis on animal proteins and fats
- A plant-based low-carb diet, with an emphasis on plant-based proteins and fats, including sugar and refined white flour, both of which are plant-based
- A healthy low-carb diet with an emphasis on plant-based proteins, healthy fats, and fewer refined grains and added sugars
- An unhealthy low-carb diet with an emphasis on animal protein, unhealthy fats, and carbohydrates from unhealthy sources such as processed breads and grains
A healthy low-carb diet was better for maintaining weight
The study found that diets consisting of plant-based proteins, fats and healthy carbohydrates were significantly associated with slower long-term weight gain than the four other eating patterns.
People who adopted the unhealthy low-carb diet as a primary strategy gained an average of about 5.1 pounds over four years, while people who adopted the healthy low-carb diet as a primary strategy lost an average of about 4.9 pounds — a total difference of 10 pounds.
These associations were strongest among participants who were younger than 55 years old, overweight or obese, less physically active, or a combination of these factors.
This study addresses an area of diet and nutrition that needed to be overhauled, says Julia Zumpano, RD, a registered dietitian at the Cleveland Clinic in Ohio. “The popularity of [low-carb diets] has increased over the past decade and initially focused on reducing carbohydrates by replacing them with meat and processed foods high in fat,” she says.
But these diets often lead to weight gain if the plan isn’t followed, due to poor food choices and overly restrictive guidelines, says Zumpano, who was not involved in the study.
“I thought the results were valid. We need to focus on diet quality, minimizing processed foods and focusing on whole foods and lean sources of protein from plant and animal sources,” she says.
Findings complement and confirm what has been seen in randomized controlled trials
This study is observational, meaning that while it shows that a healthier low-carb diet is associated with weight loss, it does not prove that eating a healthier low-carb diet caused the positive effects.
Randomized controlled trials (RCTs) of nutritional interventions are difficult to conduct, especially if they last longer than six months, because participants often do not want to change the way they eat for more than a short period of time.
Still, the study is unique and valuable because it followed so many people for 30 or even 40 years, Gardner says. This study addresses the key issue: long-term, lifetime weight maintenance – which could never be replicated in an interventional randomized controlled trial, he says.
“These findings add to the many RCTs that have reached the same conclusion: the quality of the diet is also important, not just the number of carbohydrates,” says Gardner.
Gardner co-authored a 12-month randomized controlled diet intervention, published in November 2023 in the American Journal of Clinical Nutrition which looked at people eating different types of low-carb diets. They also found that quality made a difference: the average drop in BMI was significantly greater in people who ate a higher-quality, low-carb diet, as opposed to a low-quality, low-carb diet.
Expert advice on how to follow a healthy low-carb diet
Low-carb diets can be very successful in losing and maintaining weight, especially if people eat most plant-based foods, says Zumpano. She suggests seeking help from a registered dietitian to develop a plan specifically tailored to your needs.
She offers the following nutritional recommendations to get started with healthy low-carb living.
- Non-starchy vegetables (vegetables other than potatoes, peas, and corn)
- Protein sources such as beans and lentils, and lean animal proteins such as skinless poultry, seafood, Greek yogurt, cottage cheese and eggs, and limited red meat
- Whole grains in small portions (1 cup cooked 1 to 2 times a day), such as quinoa, brown or wild rice, bulgur, or millet.
- Little to no processed foods or “low-carb” baked goods.
- Vegetable fats in the form of extra virgin olive oil, avocado oil, avocados, nuts and seeds