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Variations on the low-carb diet have been popular ways to drop pounds, but a new study shows that the quality of foods, and not just the quantity of carbohydrates, fats, and proteins, makes a difference in keeping weight off.
The research, published December 27, 2023, in JAMA Network Open, followed participants for decades to find out how five different types of low-carb diets impacted weight.
“The key takeaway from our study is that not all low-carbohydrate diets are created equal when it comes to managing weight in the long-term — the quality of the food is crucial,” says the study’s lead author, Binkai Liu, PhD, a research assistant in the nutrition department at Harvard T.H. Chan School of Public Health in Boston.
Researchers found that diets low in carbs but high in good-quality proteins, fats, and a small portion of carbs from healthful plant-based sources like whole grains and beans, were linked with slower weight gain. “On the other side, low-carb diets high in animal proteins and fats or refined carbs, such as those from red and processed meat, dairy products, and sugar-sweetened beverages, may lead to faster weight gain,” says Dr. Liu.
“This study is brilliant in terms of helping to make it clear that ‘low-carb’ is a crude term that involves a lot of oversimplification. There are many ways to eat that could 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 single approach that is 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 study.
Study Followed the Eating Patterns of 120,000 People Over 30 to 40 Years
Many studies have shown the benefits of cutting 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 non-carbohydrate restricted diets.”
But this study aimed to address a gap in knowledge, which is how well low-carb works for weight loss in the long-term, and if 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 as recently as 2018.
Participants provided self-reports of their diets and weights every four years via a survey that included more than 130 food items, with close to 70 food items containing animal protein.
The researchers scored participants’ diets according to how well they adhered to five categories of low-carbohydrate diet, all of which consisted of 30 to 40 percent carbs:
- A total low-carbohydrate diet simply focused on macronutrients that emphasized overall lower carbohydrate intake
- An animal-based low-carbohydrate diet, emphasizing animal-based proteins and fats
- A vegetable-based low-carbohydrate diet, emphasizing plant-based proteins and fats, including sugar and refined white flour, which are both plant-based
- A healthy low-carbohydrate diet emphasizing plant-based proteins, healthy fats, and fewer refined grains and added sugars
- An unhealthy low-carbohydrate diet emphasizing animal-based proteins, unhealthy fats, and carbohydrates coming from unhealthy sources such as processed breads and cereals
A Healthy Low-Carb Diet Was Better for Keeping Weight Off
The study found that diets composed of plant-based proteins and fats and healthy carbohydrates were significantly associated with slower long-term weight gain than the four other eating patterns.
People who ate the unhealthy low-carb diets as a primary strategy gained, on average, roughly 5.1 pounds over four years, whereas people who adopted the healthy low-carb diets as a primary strategy lost roughly 4.9 pounds on average — a total difference of 10 pounds.
These associations were strongest in participants who were younger than 55 years old, overweight or obese, less physically active, or some combination of these factors.
This study tackles an area of diet and nutrition that needed to be reviewed, says Julia Zumpano, RD, a registered dietitian at Cleveland Clinic in Ohio. “The popularity of [low-carb diets] has increased over the past decade and initially was focused on reducing carbs by replacing them with meats and high fat processed foods,” she says.
But these diets often lead to weight regain once the plan is not being followed, owing to poor food choices and overly restrictive guidelines, says Zumpano, who was not involved with the study.
“I found the results validating. 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’s Been Seen in Randomized Controlled Trials
This study is observational, which means that although it shows that a healthier low-carb diet is associated with keeping weight off, it doesn’t prove that eating the healthier-carb diet caused the positive effects.
Randomized controlled trials (RCTs) of dietary interventions are hard to conduct, especially those lasting more than six months, because participants often don’t 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 over 30 or even 40 years, says Gardner. This study tackles the most important issue: long-term and lifetime weight maintenance — which could never be replicated in an interventional randomized controlled trial, he says.
“These findings complement the many RCTs that have come to the same conclusion: quality of diet matters, too, not just the number of carbs,” says Gardner.
Gardner coauthored a 12-month randomized controlled dietary intervention published in November 2023 in the American Journal of Clinical Nutrition that looked at people eating different types of low carb diets. They also found that quality made a difference: The average decrease 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 Eat a Healthy Low-Carb Diet
Low-carb diets can be very successful for weight loss and maintenance, especially when people eat a majority of plant-based foods, says Zumpano. She suggests seeking help from a registered dietitian to develop a plan specific to your needs.
She offers the following food recommendations to get started on healthy low-carb living.
- Nonstarchy vegetables (veggies other than potatoes, peas, and corn)
- Protein sources like beans and lentils, and lean animal protein like 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 per day), such as quinoa, brown or wild rice, bulgur, or millet.
- Few to no processed foods or “low carb” baked goods.
- Plant-based fats in the form of extra-virgin olive oil, avocado oil, avocados, nuts, and seeds
