Do nuts make you gain weight?

Short answer

No. Across 86 trials (5,873 people), eating nuts did not raise body weight, and the calories the body actually got were 21-24% lower than calculated. A handful or two a day gave no reason to call nuts fattening.

Do nuts make you gain weight?
'Lots of fat → lots of calories → weight gain' — does this formula hold?
A handful (28 g) of almonds is 168-170 kcal by the label. Because it packs so many calories into so little food, people say to avoid nuts on a diet. We checked whether eating them actually makes you gain weight.
Pooling 86 trials
Eating nuts did not raise body weight
An analysis that pooled 86 trials with 5,873 people found the weight difference between nut eaters and non-eaters was 0.09 kg, so no gain. The certainty of the evidence was rated 'high'. Data following 569,910 people showed a 7% lower risk of reaching a body mass index of 25 or more.
Even without being told to cut other foods
Just adding nuts left weight unchanged
Another analysis of 55 trials split them by whether people were told to cut other foods to make room. Even in trials with no such advice, body weight and body fat percentage did not change. In trials with that advice, body fat percentage dropped slightly.
Why no gain? First, not all of it is absorbed
Almonds gave about 24% fewer calories than calculated
In a study where 18 people ate a set diet and even the calories in their urine and stool were measured, a handful of almonds delivered 129 kcal, about 24% less than the calculated 168-170 kcal. The calculation overstated it by 32%. In an 18-person walnut study, a handful gave 146 kcal, 21% less than the calculated 185 kcal.
Second, people ate less at later meals
The body did not burn more calories
An analysis of 27 studies with 1,121 people found that after eating nuts, people made up for it by eating less at later meals. Calories burned at rest rose by only 28.6 kcal a day, which was no real difference. The reason for no weight gain was eating less, not burning more.
Over the long run, people gained less
One extra daily serving meant about 0.26 kg less every 4 years
A study that followed 120,877 people for close to 20 years found each 1 extra daily serving of nuts went with about 0.26 kg less weight gain over 4 years. In a study of 51,188 people over 8 years, those eating nuts 2+ times a week gained 5.04 kg, versus 5.55 kg for those who rarely ate them.
Bottom line: a handful or two a day won't make you gain
Nuts did not slow weight loss on a diet either
In trials that added 28-84 g of nuts a day to a calorie-cut diet, weight loss was no different from diets without nuts. The middle intake across the 86 trials was about 45 g a day, around one and a half handfuls. That much is fine to eat without worrying about weight gain.