Eating fewer carbohydrates can slow weight gain over time. But it’s not enough to just cut back on carbs.
An analysis of data from nearly 125,000 healthy adults revealed that replacing refined carbs — white bread, white rice or sugary cereals —with whole grain foods and cutting back on animal-based fats and proteins appeared to lessen the amount of weight people gained over a four-year period, according to the report published Wednesday in JAMA Network Open.
“When it comes to a low-carbohydrate diet, quality is paramount,” said the study’s senior author, Dr. Qi Sun, an associate professor in the departments of nutrition and epidemiology at the Harvard T.H. Chan School of Public Health. “The things people need to pay attention to are high-quality carbohydrates.”
What’s in a high-quality carbohydrate diet?
- Whole grains, such as oatmeal, whole grain pasta or breads.
- Fats from vegetable oils, though not tropical ones, such as coconut or palm which are high in saturated fat.
- Plant proteins, such as beans, nuts and soy.
- Fruits.
- Vegetables.
It’s best to stay away from refined grains, like white flour, red and processed meats and saturated fats, Sun said.
The best animal protein would be fish, and then poultry, he said.
The new research adds to the growing evidence that diets heavy on healthy carbohydrates and plant-based proteins and fats are associated with significantly slower long-term weight gain.
To take a closer look at the impact of nutrient choices, Sun and his colleagues turned to three databases: the Nurses’ Health Study, which enrolled 121,700 female nurses aged 30 to 55; the Nurses’ Health Study II, which followed 116,340 females nurses who were aged 25-42 at the outset; and the Health Professionals Follow-up Study, which enrolled 51,529 male health professionals aged 40 to 75.
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For their analysis, Sun and his team focused on 123,332 men and women who had no chronic health conditions.
The researchers were not looking at very low-carb diets, like keto, Atkins or paleo.
In general, Americans tend to consume a diet that contains 50% to 60% carbohydrates, Sun said. A low-carb diet typically contains 30% to 40% carbohydrates.
The researchers scored people’s diets based on the quality of their diets and assigned them to categories based on those scores:
- Animal-based low-carbohydrate diet (ALCD).
- Vegetable-based low-carbohydrate diet (VLCD).
- Healthy low-carbohydrate diet (HLCD), which emphasized plant-based proteins, healthy fats and fewer refined carbohydrates.
- Unhealthy low-carbohydrate diet (ULCD), which emphasized animal proteins, unhealthy fats and refined carbohydrates, including processed breads and cereals.
The researchers found that when people improved the quality of their diets, they gained less weight over the four years of the study
For example, people in the healthy low-carb group whose diet scores improved the most, gained 2.1 pounds less on average compared to those who improved the least.
The two animal protein-based categories were linked to faster weight gain.
The study shows that “quality matters in a low-carb diet,” said Dr. Sahar Takkouche, an obesity expert and an assistant professor of medicine at the Vanderbilt University Medical Center in Nashville. “Healthier choices are key to better weight management.”
Even healthy choices can be made unhealthy, however, depending on how they are served. Popped corn is a good whole grain choice, unless it’s smothered in butter, sugar and salt, Sun said.
The research does have some limitations, however, Takkouche said.
Most of the participants were white women so it’s not known whether the findings would be the same for other groups. And the dietary information and people’s weights were based on self-reports, which can be flawed.
Still, the research is looking at an area — the particular foods in a low-carb diet that help slow long-term weight gain — that hasn’t been explored before, said Samaneh Farsijani, a registered dietician in the department of epidemiology at the School of Public Health at the University of Pittsburgh.
“It’s telling people that following a low-carbohydrate diet is important, but which foods they choose to consume is also important,” Farsijani said. “What I really like about this study is the emphasis on a healthy low-carb diet.”
