We all know that nuts are an incredible source of nutrition and are considered a healthy snack worldwide. Naturally rich in antioxidants, protein, healthy fats and a wide variety of vitamins and minerals, there’s no wonder that they are considered an essential part of any diet. Many people prefer to consume roasted nuts as they are generally tastier, crispier and overall more satisfying than their raw counterparts. However, are roasted nuts as healthy as raw nuts or during the roasting process do they lose some of their valuable nutrition? Let’s break down the science and get to the bottom of this question!

In general, nuts are a great source of a variety of nutrients, including antioxidants, vitamin E, magnesium and phosphorous. They are also quite high in healthy fats. Some of these nutrients are more sensitive to the roasting process than others. A good example of this is antioxidants. Antioxidants have so many different health benefits from reducing oxidative stress and cancer risk to boosting mental health and supporting healthy aging. And these are only a few of the myriad of benefits! When antioxidants are exposed to high temperatures over a certain period of time, it has been shown that the antioxidant content of that food decreases, but only up to a certain point. In a 2009 study, the antioxidant content of various nuts roasted at a temperature of 300°F for 30 minutes was tested. The result was that the levels of antioxidants found in all forms of nuts decreased steadily throughout the roasting process. But what’s interesting is that after 60 minutes of roasting, antioxidant levels of some nuts actually increased (1). The reasons for this are not well understood; however, one theory is that additional antioxidants may be formed through certain chemical reactions that happen during roasting. So, although certain antioxidants are lost, a small amount of antioxidants may also be formed during a prolonged roasting process. 

Some vitamins inherent in the nuts may also be affected by the roasting process, specifically vitamin E, thiamine (vitamin B1) and the carotenoids. These vitamins tend to be more sensitive to the heat. For example, a 2017 study found that in both almonds and hazelnuts, vitamin E levels were significantly decreased by 20% and 16% respectively compared to their raw counterparts. The study also found a direct correlation between the higher the temperature and the greater the amount of vitamin E lost (2). The same study also observed thiamine levels. Similarly to vitamin E, thiamine levels decreased during roasting and as the temperature increased, the greater amount of loss occurred. Interestingly, riboflavin (vitamin B2) levels were not affected at all by the roasting process (2). 

Variations in Nuts 

The amount of nutrients lost during roasting does not just depend on the method of roasting but also on the type of nuts that are roasted. In fact, it can be said that some nuts are slightly more sensitive to the roasting process than others. The most common roasted nuts are peanuts, almonds, pistachios and hazelnuts. Walnuts, one of the most popular nuts, is more delicate in texture. In addition, its irregular, wrinkled shape makes it more challenging to roast evenly. Walnuts are also quite high in polyunsaturated fatty acids, which makes it more susceptible to oxidation during roasting, and thus a less desirable nut both in appearance and from a health point of view. The nuts that are least likely to have their nutritional value altered during roasting are hazelnuts and pistachios, and the nuts most sensitive to roasting include both walnuts and almonds. 

In Summary

Although the nutritional value of raw and roasted nuts are not significantly different, during the roasting process some antioxidant and vitamin levels are shown to have decreased. This depends, however, on the roasting temperature, time and type of nut. 

References

1. Açar, Ö. Ç., Gökmen, V., Pellegrini, N., & Fogliano, V. (2009). Direct evaluation of the total antioxidant capacity of raw and roasted pulses, nuts and seeds. European Food Research and Technology, 229(6), 961–969. https://doi.org/10.1007/s00217-009-1131-z 
2. Stuetz, W., Schlörmann, W., & Glei, M. (2017). B-vitamins, carotenoids and α-/γ-tocopherol in raw and roasted nuts. Food Chemistry, 221, 222–227. https://doi.org/10.1016/j.foodchem.2016.10.065