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 [2].

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 [2]:

  • 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 [3, 4]
    • Healthy fats in nuts help release satiety hormones cholecystokinin (CCK) and peptide YY (PYY), which help to tell you when you’re full [5, 6]
  • 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 [7]
  • 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) [8] 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. Neale, E., et al., The effect of nut consumption on heart health: an updated systematic review of the literature. 2018. Nuts for Life, unpublished.
  3. Noakes, M., The role of protein in weight management. Asia Pac J Clin Nutr, 2008. 17 Suppl 1: p. 169-71.
  4. 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.
  5. 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.
  6. 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.
  7. Mattes, R.D., The energetics of nut consumption. Asia Pac J Clin Nutr, 2008. 17 Suppl 1: p. 337-9.
  8. 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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