Research consistently shows that nuts do not lead to short-term weight gain and support better weight management over the long term (1). Despite this, concerns about nuts contributing to weight gain persist among both the public and some health professionals.

It’s time to set the record straight.

The scientific truth about nuts and weight:

• At least 19 systematic literature reviews show (convincingly) that nuts do not cause weight gain.
• In fact, research suggests that even higher intakes (above 30g/day) support less weight gain, and
• Sustained, long-term intake of nuts is associated with improved weight outcomes (4).

Summary of the key evidence:

Randomised controlled trials (short-term research)

Convincing evidence shows that nut consumption does not increase body weight.

The largest and most comprehensive systematic literature review (SRL) on nuts and body weight included 86 randomised controlled trials (RCTs) and six prospective cohort studies (1). A meta-analysis (MA) was conducted, and the certainty of the evidence was assessed using the Grading of Recommendations Assessment, Development, and Evaluation (GRADE) tool.

The 86 RCTs in this review had a median study duration of eight weeks.

Table 1: Summary of the findings from the SLR and MA of 86 RCTs

High-certainty data from RCTs confirm neutral weight effects when nuts are added to the diet, even without calorie offsets.

Seventeen other SLRs have also explored the relationship between nut consumption and body weight in the short-term. All the findings have been consistent: that nuts do not increase body weight.

This includes:

• Established SLR evidence from 10+ years ago: Two of the earliest SLRs, conducted in 2013 (2) and 2018 (3), each reported no adverse effects of nuts on body weight in RCTs.

• Studies using (or not using) dietary substitutions: A 2021 SLR and MA investigated the effect of dietary substitution with nuts and body weight (4). Both in studies with dietary substitution instructions (for example, replacing current snacks with nuts), and without dietary substitution instructions (for example, adding nuts to the diet), it found no change in body weight.  

• Research involving health conditions: Three recent SLRs with MA published between 2022 to 2025 focused specifically on people with type 2 diabetes (5), people on restrictive energy diets (6), or people with atherosclerotic cardiovascular disease (7). Each study reported no adverse effects of nuts on body weight.

Did you know? There’s a six-fold difference between ‘actual’ and ‘target’ nut intake – which is the largest shortfall of any food group (8). Fear of weight gain, due to concerns about the energy content of nuts, is a major barrier to consumption (9).

Prospective cohort studies (long-term research)

Long-term studies show that people who eat nuts regularly gain less weight over time.

A MA, of six prospective cohort studies (which had a median follow-up duration of 18 years), found nuts were linked with a 7% lower incidence of overweight/obesity (1). The certainty of this evidence using GRADE was ‘moderate’.

In these long-term studies, higher nut intake was linked with:

• ↓ BMI gain
• ↓ Weight gain
• ↓ Waist circumference gain

These results are supported by an earlier SLR (10), which showed higher nut intake was associated with less weight gain and a lower risk of overweight/obesity.

The largest ever review on nuts and weight found eating more nuts, over a longer period, was linked to lower body weight (1).

What about nut portion size and weight?

Higher nut intakes are linked to modest reductions in body weight and fat mass.

The effect of nut portion size has recently been investigated in a SLR and MA (1).

Looking at the RCTs within this review, researchers conducted a sub-analysis by dose to compare intervention studies with <45.5g of nuts, to those with ≥45.5g. This showed significant differences between sub-groups for body weight and BMI, with increased body weight and BMI in studies with smaller nut doses (<45.5g).

Taking this a step further, the researchers also conducted a meta-regression to analyse the link between nuts and portion size across the full range of nut intakes.

In the RCTs, each 30g per day increase in nut intake was linked with:

• ↓ 0.36kg body weight
• ↓ 1.05% body fat

In the prospective cohort studies, people who had higher intakes of nuts had a lower risk of developing overweight/obesity, were less likely to gain 5 kg or more of weight and had lower increases in waist circumference over time.

Across all studies, there was no strong evidence of a ‘tipping point’ when it came to very large portion sizes of nuts and weight increases. Even in individual studies providing 100g of nuts per day (>3 handfuls), no weight gain was reported.

The bottom line:

Research consistently shows that eating nuts does not lead to weight gain. Even larger servings (100g or around 3 handfuls a day) do not increase weight. And long-term studies show that people who eat nuts regularly have a lower risk of becoming overweight or obese.

Health professionals can use this evidence to counter outdated ‘nut-calorie-weight’ concerns – recommending at least a handful of nuts a day, including for weight-conscious clients or patients.

Did you know? An umbrella review, published in 2025, on food groups and body weight, reinforced that nuts promote healthy weight and sit alongside whole grains, legumes, fruits, and vegetables when it comes to food groups that support body weight outcomes (11).