Weight loss is a common goal, and there is no shortage of diets claiming to provide the best solution.
One of the most persistent debates is whether a low-fat or low-carbohydrate approach is more effective.
What did the DIETFITS study find?
The DIETFITS randomised clinical trial compared a healthy low-fat diet with a healthy low-carbohydrate diet over 12 months. The study involved 609 adults who were overweight or living with obesity.
Participants in both groups were encouraged to maximise vegetables, choose minimally processed whole foods and prepare meals at home where possible. They were advised to limit refined flour, added sugar and highly processed foods. They were not given a fixed calorie target.
After 12 months, there was no significant difference in weight loss between the two groups. Average weight loss was approximately 5.5 to 6 kilograms in both.
Although strict calorie targets were not prescribed, average energy intake decreased in both groups. This suggests that improving food quality and eating habits may naturally influence the amount of energy consumed.
Diet quality and adherence matter
A later analysis of the same trial found that participants who combined better dietary quality with stronger adherence tended to achieve greater reductions in body mass index, regardless of whether they followed the healthy low-fat or healthy low-carbohydrate approach.
This supports an important practical point: the label attached to a diet may matter less than its nutritional quality and whether it can be followed consistently.
Both approaches in the trial emphasised vegetables and whole foods rather than simply reducing one macronutrient while ignoring the overall diet.
There is no single perfect diet
Weight loss requires an energy deficit over time, but this does not mean everyone must count every calorie.
Different people may find different dietary patterns easier to maintain. Preferences, culture, work, family routine, medical conditions, hunger, food access and exercise levels all influence what is realistic.
A sustainable approach should support adequate nutrition and long-term health rather than producing only a brief change on the scales.
Exercise and physical activity can support weight management, fitness and the maintenance of lean muscle, but they are only one part of the picture.
For personalised dietary advice—particularly where medical conditions, medications or substantial weight change are involved—guidance should be obtained from a doctor or Accredited Practising Dietitian.
The takeaway
The DIETFITS study did not identify either a healthy low-fat or healthy low-carbohydrate diet as clearly superior for weight loss.
The more useful focus is on food quality, a sustainable reduction in energy intake and habits that can be maintained over time. Unfortunately, there is no magic diet.
References
- Gardner CD, Trepanowski JF, Del Gobbo LC, et al. Effect of low-fat versus low-carbohydrate diet on 12-month weight loss in overweight adults and the association with genotype pattern or insulin secretion: the DIETFITS randomized clinical trial. JAMA. 2018;319(7):667–679.
- Hauser ME, et al. Dietary quality and adherence in relation to 12-month weight change: a secondary analysis of the DIETFITS randomized clinical trial. The Journal of Nutrition. 2024.