crunching the numbers on nuts.

Recently, a GP (who knew I was a nutrition scientist) confidently told me that nuts were too high in calories to be a ‘sensible snack’. After all, there can be as many calories in a handful of nuts as there are in a chocolate bar...

This isn’t the first time I’ve heard this. Nuts have long carried a reputation as a “fattening food,” since they are high in fat, even though they are ‘good’ fats, and even though nuts are a core, whole food.

While limiting nuts seems logical and aligned with the routine messages stating that nutrient-dense foods should be encouraged, and energy-dense foods should be reduced, food and nutrition science is rarely simple, and simple logic often doesn’t stack up to the evidence.

So, what DOES the evidence say about nuts and weight?

The weighty truth

The most comprehensive research comes from systematic reviews and meta-analyses, which combine results from many trials. A 2020 review of 55 randomised controlled trials (RCTs) found that adding nuts to people’s diets did not lead to increases in body weight, body mass index (BMI), or waist circumference.

Another systematic review with meta-analysis of 86 RCTs and 6 unique cohorts to the same conclusion: nut consumption is either neutral or protective when it comes to weight gain.

Importantly, these findings held true even when people ate more than the standard 30-gram “handful” standard serve we tend to recommend, with people who ate more losing more weight.

Evidence from long-term population studies points in the same direction. In the US Nurses’ Health Study and Health Professionals Follow-up Study, people who ate nuts regularly gained less weight over 20 years and had a lower risk of obesity.

Taken together, this body of research challenges the common belief that eating nuts inevitably leads to weight gain.

The vanishing calorie

If nuts are so energy-dense, why don’t they pile on the kilos?

One reason is satiety. Nuts contain a unique combination of protein, fibre, and healthful fats, which may help reduce the likelihood of overeating later. Controlled feeding trials show that when people snack on nuts, they unconsciously eat less at subsequent meals, offsetting as much as 75% of the energy the nuts provide.

Another factor is digestibility. Not all of the fat in nuts is absorbed by the body. Much of it is locked inside rigid plant cell walls that our digestive enzymes can’t fully break down. As a result, some fat travels through the gut and is excreted, never contributing to our energy intake.

The calories (or kilojoules) on nutrition labels come from an old system that looks at the amount of energy released from foods when burned (calorimetry), adjusted for estimated losses in feces, urine, gases and other secretions calculated from human feeding experiments. More modern studies suggest that the metabolisable energy of nuts is 5-25% lower than what standard nutrition labels suggest. This means the “true” energy contribution of nuts is smaller than it appears on paper.

This doesn’t necessarily mean that we shouldn’t trust labels, but it does mean we should acknowledge that these numbers aren’t precise, and human digestion is complex and variable.

The metabolic advantage

Nuts may not just be neutral for weight; they might actively support metabolic health in ways that reduce the risk of weight gain over time.

For example, nuts are rich in dietary fibre and polyphenols, which act as fuel for beneficial gut bacteria. Research shows nut consumption can increase microbial diversity and promote bacteria linked to improved metabolism.

Nuts also contain bioactive compounds with anti-inflammatory properties. Chronic low-grade inflammation is thought to play a role in weight gain and obesity. By reducing inflammatory markers, nuts may help protect against this.

Finally, nuts improve how the body handles glucose and insulin. A systematic review found that nut consumption improves glycaemic control in people with and without diabetes. Better insulin sensitivity helps the body use energy more effectively, making it less likely to be stored as fat.

These effects combine to create what some researchers call a “metabolic advantage”, with the suggestion that nuts support underlying processes that help keep weight stable in the long term.

Why do people still worry about nuts and weight?

If the evidence is clear, why does the belief persist? Part of the answer lies in what psychologists call the “unhealthy = tasty” intuition.

This is the common and often subconscious assumption that foods that taste good must be bad for us, while healthy foods are assumed to be bland or unsatisfying. Nuts, with their rich texture and high fat content, are delicious, and that might trigger this intuition.

But in this case (as is often the case), the ‘intuition’ is misleading. Nuts can be both tasty and healthy, offering satiety, nutrient density and long-term health benefits without the expected weight gain.

While the evidence shows nuts aren’t linked with weight gain, it’s worth reflecting on why this point gets so much attention. For decades, nutrition messages have been shaped by fear of fatness - a fear that has more to do with cultural stigma than with health itself. This framing risks reinforcing harmful ideas that weight gain is always negative, when in reality body size is not a straightforward measure of health.

It’s also important to remember that energy itself is essential. Calories aren’t the enemy, they’re what fuel our bodies to think, move, repair, and thrive. The focus should not be on avoiding energy, but on choosing foods that deliver it alongside nutrients that support long-term wellbeing.

Nuts are a perfect example: they provide protein, fibre, healthy fats, vitamins and minerals. These benefits hold true across body sizes. So rather than focusing on nuts as a food that won’t ‘make you fat,’ it may be more accurate, and less harmful, to say nuts are a nutrient-dense source of energy that supports health in many ways.

The bottom line

Nuts don’t defy the laws of physics; energy balance still matters. But foods and humans aren’t just physics; eating sees a complex biological food interacting with a complex biological human within complex environments. The unique properties of nuts mean they can behave differently in the body than physics might have us expecting. You are not a spreadsheet, and as long as you don’t have allergies, nuts can (and maybe even should) be part of a healthy, balanced diet.

I learned alot of this from my colleagues at FOODiQ Global - Tim Cassettari and Carlene Starck, PhD. Tim recently presented a webinar for Dietitian Connection called Reframing the calorie equation that you might want to catch up on. This work was supported by Nuts for Life. All opinions are my own.