By Paul McClure
A study comparing low-carb diets has found that not all eating plans are created equal
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Researchers have done a deep dive into five low-carbohydrate diets emphasizing different nutrients and their quality to see which eating plans provides better long-term results regarding weight change. Their findings highlight the importance of diet quality when eating low-carb to maintain a healthy body weight.
Those with a New Year’s resolution to start eating better may have considered a low-carbohydrate diet. Some evidence suggests that a low-carb diet can improve metabolic health and help people lose weight more quickly than a low-fat eating plan. However, little research has been conducted on the effect of a low-carb diet on long-term weight maintenance.
In a new study, researchers from the Harvard T.H. Chan School of Public Health have compared five low-carbohydrate diets, each emphasizing different macronutrient components and the quality of those macronutrients, to see which was better for long-term weight change.
“Our study goes beyond the simple question of, ‘To carb or not to carb?’” said Binkai Liu, the study’s lead author. “It dissects the low-carbohydrate diet and provides a nuanced look at how the composition of these diets can affect health over years, not just weeks or months.”
The researchers used data from three large ongoing prospective US studies, the Nurses’ Health Study (NHS), Nurses’ Health Study II (NHSII), and Health Professionals Follow-up Study (HPFS), and analyzed the diets and weights of 123,332 healthy adults between 1986 and 2018. The mean age of participants was 45; 83.8% were female. Each participant provided self-reports of their diets and weights every four years.
The researchers scored participants’ diets based on how well they adhered to five categories of low-carb diets (LCDs): total low-carb diet (TLCD) that emphasized overall lower carbohydrate intake; animal-based low-carb diet (ALCD), emphasizing animal-based proteins and fats; vegetable-based low-carb diet (VLCD), emphasizing plant-based proteins and fats; healthy low-carb diet (HLCD) that emphasized plant-based proteins, healthy fats, and fewer refined carbohydrates; and unhealthy low-carb diet (ULCD) that emphasized animal proteins, unhealthy fats, and carbs coming from unhealthy sources like processed bread and cereals.
The researchers devised an LCD score ranging from zero to 30, with a higher score indicating greater adherence to the given diet. The primary outcome of interest was four-year changes in score, which was calculated by subtracting the scores at the start of each four-year interval from the score at the end of the four-year interval. They did the same thing concerning the participants’ weight change.
The researchers found that results across the three study cohorts were largely consistent: increasing TLCD, ALCD, and ULCD scores were each associated with more weight gain and an increasing HLCD score was associated with less weight gain. These associations were most pronounced for participants under 55, overweight or obese, and/or less physically active. The results for VLCD were ambiguous across the cohorts. In NHSII, changing to more adherence to VLCD was significantly associated with less weight gain, while the association was less clear in NHS and HPFS.
These findings suggest that the quality of low-carb diets may play a critical role in long-term weight change. Only those diets that emphasized high-quality protein, fat, and carbohydrates from whole grains and other plant-based foods were associated with less weight gain.
“The key takeaway here is that not all low-carbohydrate diets are created equal when it comes to managing weight in the long term,” said Qi Sun, one of the study’s co-authors. “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 researchers point to some of their study’s strengths. Namely, they created five versions of low-carb diets based on macronutrient quality and amount, which provided a broader scope for examining the association between the eating plan and weight change. And the large sample sizes and long-term follow-up allowed them to explore that association with relatively large statistical power. However, the self-reported nature of the data lends itself to measurement errors. And the study didn’t measure body composition, so the researchers couldn’t ascertain how the diets impacted lean body mass and body fat. The large proportion of white participants may limit generalizability.
Nonetheless, the study underscores the importance of diet quality when eating low-carb for weight management. The researchers suggest that future research validate these findings in more diverse populations and explore the mechanisms underlying these associations.
The study was published in the journal JAMA Network Open.
Source: Harvard T.H. Chan School of Public Health
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