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A recent study from the Harvard School of Public Health highlights the importance of the quality of macronutrients (e.g., fat and protein) in low-carbohydrate diets over simply reducing carbohydrate intake.

Published in JAMA Network Open, the study explored how different types of low-carb diets affect long-term weight change among US adults. The researchers wanted to better understand how the quality of macronutrients affects weight outcomes amongst people on low-carb diets.

The study analysed data from three large ongoing cohorts: the Nurses’ Health Study (NHS), the Nurses’ Health Study II (NHSII), and the Health Professionals Follow-up Study (HPFS), including over 123,000 participants. Since recruitment (in 1976 for the NHS, 1989 for the NHSII, and 1986 for the HPFS), researchers have regularly followed up with participants and assessed their diet every 4 years using a validated semiquantitative food frequency questionnaire. In this study, the researchers looked at weight changes over 20 years of follow-up.

Based on the food frequency questionnaire data, the researchers gave participants a diet score according to how closely they adhered to one of the following low-carbohydrate diets:

  • Total Low-Carbohydrate Diet (TLCD) emphasising an overall lower carbohydrate intake
  • Animal-Based Low-Carbohydrate Diet (ALCD) further emphasising animal sources of protein and fat
  • Vegetable-Based Low-Carbohydrate Diet (VLCD) further emphasising plant sources of protein and fat
  • Healthy Low-Carbohydrate Diet (HCLD) emphasising less refined carbohydrates (i.e., less refined starches and sugars), and more plant protein and healthy fat
  • Unhealthy Low-Carbohydrate Diet (ULCD) emphasising less carbohydrate from healthful sources, and more animal protein and unhealthy fat

Researchers measured weight changes every 4 years and analysed the relationship with adherence to different dietary patterns.

The study found that, on average, participants gained weight over the study periods. However, the amount of weight gain varied depending on which LCD dietary pattern they most closely followed. After adjusting for demographics and other lifestyle factors that may affect weight gain, the researchers found that following a low-carb diet, particularly an animal-based or unhealthy low-carb diet, was associated with more weight gain, while vegetable-based and healthy low-carb diets were associated with less weight gain. These associations were stronger in those who were carrying excess weight.

The researchers concluded that the quality of low-carb diets may play an important role in long-term weight change and that only low-carb diets that emphasise plant protein, healthy fats and minimally processed carbohydrates are associated with less weight gain.

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Dr Kate Marsh is an is an Advanced Accredited Practising Dietitian, Credentialled Diabetes Educator and health and medical writer with a particular interest in plant-based eating and the dietary management of diabetes and polycystic ovary syndrome (PCOS).

Contact: Via her website www.drkatemarsh.com.au