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Low-carb vs low-fat diets

When calories and protein are similar, low-carbohydrate and low-fat diets produce about the same fat loss over a year or more. Neither has a meaningful metabolic advantage, so the better diet is the one you can stick to.

What the science says

  • Same 12-month weight loss Strong evidence

    In the DIETFITS trial (Gardner et al., 2018), 609 adults with overweight lost 5.3 kg on a healthy low-fat diet and 6.0 kg on a healthy low-carbohydrate diet at 12 months, a non-significant difference. Neither genotype pattern nor insulin secretion predicted who did better on which diet.

  • The macro mix did not matter over two years Strong evidence

    In POUNDS Lost (Sacks et al., 2009), 811 adults on diets with 35–65% of calories from carbohydrate and 20–40% from fat lost similar weight at 2 years (about 3–4 kg).

  • No metabolic advantage for cutting carbohydrate Moderate evidence

    Hall and Guo's 2017 meta-analysis of 32 controlled feeding studies that swapped carbohydrate for fat at equal calories found slightly greater energy expenditure (26 kcal/day) and fat loss (16 g/day) with lower-fat diets, the opposite of the carbohydrate-insulin prediction, though the differences are tiny.

  • Low-fat eating led to fewer calories in one inpatient study Limited evidence

    Hall et al. (2021) gave 20 inpatients an unlimited plant-based low-fat diet and an animal-based ketogenic diet for 2 weeks each. They ate about 690 kcal/day less on the low-fat diet. The study was short and small.

How to apply it

Pick the macro split you can sustain, keep protein high, and let the calorie deficit do the work.

Protein (either diet)About 1.6–2.4 g/kg/day
Low-carb versionMostly vegetables, protein foods, nuts and olive oil; carbohydrate around 30% of calories or less
Low-fat versionMostly whole grains, legumes, fruit, vegetables and lean protein; fat around 20–30% of calories
If you lift hardKeep enough carbohydrate around training to sustain performance

Who should be careful

Both approaches are safe for healthy adults when built from whole foods. People taking diabetes or blood-pressure medication must not start a very-low-carbohydrate diet without medical supervision, because doses may need adjusting. Anyone with diabetes, high blood pressure or another obesity-related condition, a history of eating disorders, who is pregnant or breastfeeding, or who is considering weight-loss medication should plan weight loss with a physician or registered dietitian; this page gives no drug advice.

Frequently asked questions

Is low-carb better than low-fat for losing weight?

No. In DIETFITS, 609 adults lost 6.0 kg on low-carb and 5.3 kg on low-fat at 12 months, a non-significant difference.

Can my genes or insulin tell me which diet suits me?

Not in DIETFITS: neither genotype pattern nor insulin secretion predicted who lost more on either diet.

Doesn't cutting carbs lower insulin and burn more fat?

Controlled feeding studies do not support that. A meta-analysis of 32 of them found slightly more fat loss with lower-fat diets at equal calories, although the difference was tiny.

Scientific references

More on weight loss

  • Rate of weight loss Moderate evidence

    For people who lift, losing about 0.

  • Resistance training while dieting Strong evidence

    Lifting weights during a diet makes much more of the weight you lose come from fat instead of muscle, and it keeps or raises strength.

  • Cardio for weight loss Moderate evidence

    Cardio helps fat loss, but at typical doses it produces only a couple of kilograms on its own; clinically meaningful loss takes high volumes (more than about 250 minutes a week) or a calorie deficit alongside it.

  • Diet breaks and refeeds Moderate evidence

    Planned periods at maintenance calories in the middle of a diet are at least as effective as dieting continuously and may make the diet easier to tolerate.

  • Intermittent fasting Moderate evidence

    Intermittent fasting (5:2, alternate-day fasting or time-restricted eating) works for weight loss about as well as an ordinary calorie-controlled diet, but not better.

  • Self-monitoring (food logging and weighing) Moderate evidence

    Tracking what you eat and weighing yourself regularly are consistently linked to more weight loss and less regain.