Because nuts are an energy dense food with a high fat content, there is a widespread perception that eating nuts causes weight gain.
But decades of research show that this is not true. Nuts are actually associated with a decreased  risk of being overweight or obese, and regularly eating nuts reduces body weight, body mass index (BMI) and waist circumference [1]

How do nuts help manage weight?

  • An abundance of healthy fats, fibre and protein mean nuts satisfy hunger and reduce your appetite. A handful of nuts releases satiety hormones in the digestive system which help tell you when you’re full [2, 3].
  • The fibrous cell walls in nuts stop our bodies absorbing up to 15% of the kilojoules (or calories) in nuts [4-6].
  • Eating nuts can significantly reduce the number of calories consumed at later meals – i.e. you’ll eat less [7].
  • Regularly eating nuts can boost your resting metabolic rate by 5-10%, meaning that your body is burning more kilojoules (or calories).

A serve of nuts is 30g, or about one handful. And we should all aim to eat at least one handful every day. But there’s no reason why you can’t eat more. Research suggests that around two handfuls (60g) each day helps lower cholesterol [8], and that you can eat up to 120g nuts each day without gaining weight [1].

Studies have been conducted on many different tree nuts. The take out? All nuts have a positive effect on weight, so enjoy a variety of nuts every day. However, it’s best to enjoy raw or roasted, unsalted nuts as your everyday choice, saving salted nuts for special occasions.

What the research says

Because nuts are an energy dense food with a high fat content, there is a widespread perception that their consumption leads to unwanted increases in body weight.

This is despite two very large studies – Adventist Health study (1992) and Nurses’ Health Study (1998) showing significant inverse associations between the frequency of nut consumption and body mass index (BMI). 
Evidence from a systematic literature review and meta-analysis of 3 prospective cohort studies and 62 randomised controlled trials shows that nuts are associated with reduced overweight/obesity and that a diet enriched with nuts reduces body weight, body mass index and waist circumference [1].

Another recent review which found non-significant reductions following nut consumption for all anthropometric outcomes, except waist circumference where significant reductions were found [9].

Risk of overweight/obesity

Each increased increment of 30-gram serving/week in nut consumption was associated with a 3% reduced risk of overweight/obesity [1].

Changes in body weight parameters

A nut-enriched diet was associated with significant reductions in body weight parameters compared to a controlled diet in randomised trials [9]:

  • Decrease in body weight (-0.22kg)
  • Decrease in BMI (-0.16kg/m2)
  • Decrease in waist circumference (10.51cm)

How many nuts and for how long?

  • The duration of clinical trials varied from 2 to 336 weeks.
  • The median dose of tree nuts ranged from 10 to 120 grams per day.

Potential mechanisms of action

There are several ways that nuts can help manage weight:

  • Nuts can enhance satiety and reduce appetite 
    • Protein and fibre in nuts help satisfy hunger and reduce appetite [10, 11]
    • Healthy fats in nuts help release satiety hormones cholecystokinin (CCK) and peptide YY (PYY), which help to tell you when you’re full [2, 3]
  • Increasing resting energy expenditure
    • Metabolism increases immediately after eating nuts, and this increase can account for up to 10% of the energy the nuts contain [12]
  • Poor bio-accessibility of the energy they provide, leading to inefficient energy absorption
    • The digestion and absorption of the kilojoules (energy) in nuts is incomplete. It has been suggested that up to 15% of the energy in nuts is not absorbed and is excreted. 
  • The energy provided by nuts is offset by spontaneous adjustments in the total diet
    • Nut consumers ate significantly less energy at their next meal (by up to as much energy as the nuts provided) [13] which may be due to the abundance of healthy fats, protein and fibre
  • Prebiotic effects on the gut microbiome that could be important for weight management.

References

  1. Li, H., et al., Nut consumption and risk of metabolic syndrome and overweight/obesity: a meta-analysis of prospective cohort studies and randomized trials. Nutr Metab (Lond), 2018. 15: p. 46.
  2. Cassady, B.A., et al., Mastication of almonds: effects of lipid bioaccessibility, appetite, and hormone response. Am J Clin Nutr, 2009. 89(3): p. 794-800.
  3. Pasman, W.J., et al., The effect of Korean pine nut oil on in vitro CCK release, on appetite sensations and on gut hormones in post-menopausal overweight women. Lipids Health Dis, 2008. 7: p. 10.
  4. Mandalari, G., et al., The effects of processing and mastication on almond lipid bioaccessibility using novel methods of in vitro digestion modelling and micro-structural analysis. Br J Nutr, 2014. 112(9): p. 1521-9.
  5. Ellis, P.R., et al., Role of cell walls in the bioaccessibility of lipids in almond seeds. Am J Clin Nutr, 2004. 80(3): p. 604-13.
  6. Novotny, J.A., S.K. Gebauer, and D.J. Baer, Discrepancy between the Atwater factor predicted and empirically measured energy values of almonds in human diets. Am J Clin Nutr, 2012. 96(2): p. 296-301.
  7. Hull, S., et al., A mid-morning snack of almonds generates satiety and appropriate adjustment of subsequent food intake in healthy women. Eur J Nutr, 2015. 54(5): p. 803-10.
  8. Sabate, J., K. Oda, and E. Ros, Nut consumption and blood lipid levels: a pooled analysis of 25 intervention trials. Arch Intern Med, 2010. 170(9): p. 821-7.
  9. Neale, E., et al., The effect of nut consumption on heart health: an updated systematic review of the literature. 2018. Nuts for Life, unpublished.
  10. Noakes, M., The role of protein in weight management. Asia Pac J Clin Nutr, 2008. 17 Suppl 1: p. 169-71.
  11. Pereira, M.A. and D.S. Ludwig, Dietary fiber and body-weight regulation. Observations and mechanisms. Pediatr Clin North Am, 2001. 48(4): p. 969-80.
  12. Mattes, R.D., The energetics of nut consumption. Asia Pac J Clin Nutr, 2008. 17 Suppl 1: p. 337-9.
  13. Tan, S.Y., J. Dhillon, and R.D. Mattes, A review of the effects of nuts on appetite, food intake, metabolism, and body weight. Am J Clin Nutr, 2014. 100 Suppl 1: p. 412s-22s.
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