There are some very minor nutritional differences between raw, dry roasted and oil roasted nuts. Most nutrients – particularly minerals – become more concentrated during the roasting process as moisture is lost, meaning that roasted nuts have less water and a slightly higher concentration of minerals. B group vitamins and vitamin E are not heat stable, so these are slightly reduced in roasted nuts. The fat content of oil roasted nuts increases by only around 5% compared to raw nuts. This is because nuts absorb very little of the oil that they are roasted in.

Both raw and roasted nuts (whether dry or oil roasted) have a similar nutrient composition, although there are some small differences [1-5]. Most nutrients – particularly minerals – become slightly more concentrated during the roasting process as nuts lose some moisture. The B group vitamins are not heat stable so their levels are reduced after roasting. Vitamin E can also be reduced by roasting and the amount depends on the nut variety and the length of time being roasted. A light roasted colour is best for both sensory properties and nutrition.

Nuts are naturally high in healthy fats so they are unable to absorb much more fat, even if they’re oil roasted. As a result, the total fat of raw and oil roasted nuts varies only by an average of around 5% [6] Finally, there is some evidence to suggest that a negligible amount of trans fats are produced after roasting, but this is dependent on the time and temperature of the roast. Despite this, the amount of trans fat is only just measurable between 0.07-0.9%. 

It’s worth keeping in mind that despite these very small differences, epidemiological evidence links eating nuts with a reduced risk of heart disease by around 40% [7, 8]. These studies don’t distinguish between raw and roasted nuts, with participants likely to be eating a mixture of both.

References

  1. Alasalvar, C., E. Pelvan, and B. Topal, Effects of roasting on oil and fatty acid composition of Turkish hazelnut varieties (Corylus avellana L.). Int J Food Sci Nutr, 2010. 61(6): p. 630-42.
  2. Amaral, J.S., et al., Effects of roasting on hazelnut lipids. J Agric Food Chem, 2006. 54(4): p. 1315-21.
  3. Stuetz, W., W. Schlormann, and M. Glei, B-vitamins, carotenoids and alpha-/gamma-tocopherol in raw and roasted nuts. Food Chem, 2017. 221: p. 222-227.
  4. Yaacoub, R., et al., Formation of lipid oxidation and isomerization products during processing of nuts and sesame seeds. J Agric Food Chem, 2008. 56(16): p. 7082-90.
  5. Schlormann, W., et al., Influence of roasting conditions on health-related compounds in different nuts. Food Chem, 2015. 180: p. 77-85.
  6. United States Department of Agriculture USDA. Food Composition Databases.
  7. Kelly, J.H., Jr. and J. Sabate, Nuts and coronary heart disease: an epidemiological perspective. Br J Nutr, 2006. 96 Suppl 2: p. S61-7.
  8. Aune, D., et al., Nut consumption and risk of cardiovascular disease, total cancer, all-cause and cause-specific mortality: a systematic review and dose-response meta-analysis of prospective studies. BMC Med, 2016. 14(1): p. 207.
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