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

This is one of the most heavily studied questions in weight research, and the answer is unusually consistent. DIETFITS, one of the largest head-to-head comparisons ever run, randomised 609 adults to either a healthy low-fat diet or a healthy low-carbohydrate diet for twelve months. The low-fat group lost 5.3 kg on average and the low-carb group 6.0 kg. The 0.7 kg difference was not statistically significant. The study also tested whether genotype or insulin secretion could predict which diet suited whom. Neither could.

The meta-analyses land in the same place. Johnston and colleagues compared named diets across 48 randomised trials with 7,286 participants: at six months, low-carb diets produced 8.7 kg and low-fat diets 8.0 kg compared with no diet, and at twelve months the figures were practically identical, 7.25 versus 7.27 kg. The authors' conclusion was to recommend whichever diet the person can actually follow. Tobias and colleagues pooled 53 studies with over 68,000 participants and found a small advantage for low-carb, just over one kilo after at least a year. It is real but small, and low-fat diets were no better than other comparison diets of similar intensity.

Ge and colleagues, in a network meta-analysis of 121 trials with nearly 22,000 participants, found that at six months low-carb and low-fat produced almost exactly the same result, 4.6 and 4.4 kg more than a usual diet, and that by twelve months most of the effect had faded regardless of approach.

The pattern is clear: both work when they create a calorie deficit. The difference between them is small compared with the difference between sticking to a plan and not sticking to one.

The diet wars have run for decades, and both camps have something to sell. Books, programmes and products market best with a winning formula; an honest "pick what you can sustain" sells worse than "carbs are the enemy" or "fat makes you fat". Single-cause explanations also feel more scientific than they are: the insulin hypothesis and fat phobia each point to one villain, and one villain implies one simple solution you can buy. Add confirmation bias. Someone who lost weight on low-carb gives cutting carbs all the credit, not the calorie deficit the diet created, and passes the story on. And since the debate itself generates clicks and engagement, it stays alive long after the research has settled.

Pick the split you actually enjoy. If you like bread, rice and fruit, you don't need to remove them; if you prefer fewer carbs and more fat, that works too. Keep protein sufficiently high, create a moderate calorie deficit, and spend your energy on what actually decides the outcome: an approach you can live with for months, not weeks. If you want to see what a sensible split looks like in grams for you, you can calculate it.