I like roasted nuts as a snack. But I also like the nutrition of nuts, and wonder how much that nutritional value is compromised by roasting. Do they become empty calories, or do their health benefits remain largely intact even after roasting?
The basic reason of cooking is to make nutrients more readily available. While some vitamins may be modified into un-usability, other nutrients in nuts aren’t just intact: they’re more absorbable than if you ate them raw. Determining the nutritional values of food is a whole scientific field, but in any case, you should search for specific info on the exact nuts and techniques you’re worried about. Some modern industrial techniques which aren’t readily available to a home cook are used in part because they preserve nutritional values better (mainly proteins, which aren’t much of a worry in a relatively-low-protein solid, and some vitamins).
I remembered something about the fat, so I googled, and this was what came up:
Nuts do not lose their heart-healthy monounsaturated fat during the roasting process. However, roasting may alter and damage the polyunsaturated fats that nuts also contain and that are more vulnerable to oxidation. … Roasted, chopped, and ground nuts go rancid more quickly than whole raw ones
Other the breakdown of polyunsaturated fats and dehydration, light roasting and mechanical processing (chopping and blending) of nuts has relatively little effect on the nutrients of nuts and other seeds. The nutrients in various nuts are primarily monounsatured fats, folate (vitamin B9), various Vitamin E complexes (tocopherols and tocotrienols), calciumm iron, manganese, potassium, selenium, thiamin, some essential amino acids, and a small amount of fiber. While nuts are calorically dense (since most of their calories come from fats) they are the opposite of “empty calories”, which is really a term that should be reserved for sugars and starchy carbohydrates. Roasted nuts will become rancid more quickly than raw nuts unless stored in an airtight container but in general nuts store very well, hence why animals collect them for winter stores.
Most canned “roasted” nuts are actually deep fried in oil, but because they are not very porous and contain only a small amount of water to be offset, they don’t actually absorb much of the fats. Unlike the cooking of animal protein or fiberous plant materials, roasting or other cooking methods do little to make the nut more digestible—most nuts have a relatively high fat content and are already easily digestible—but it can destroy toxic compounds such as the hydrogen cyanide that can be found in bitter almonds. (Yes, as a member of Prunus, almonds are not a “true nut”, pedants.) However, all modern cultivars of nuts and seeds sold for human conspumption today have been bred to have only trace amounts of poisonous substances such that even massive overconsuption would be below a toxicity threshold.
It should be noted that some raw nuts and seeds can carry Enterobacteriaceae pathogens like Salmonella enterica and Escherichia coli and freezing or washing the nuts will not render them safe for consumption. This can be true with cooked nuts as well if they are contaminated after the roasting process, so if you get a suspect batch of nuts its better to toss them.
Roasted nuts, and particularly those roasted or fried in oil can contain acrylamide, a possible human carcinogen, developed during the cooking process. The same is true for pretty much anything fried, sauteed, or roasted in oil above 250 °F, and the amount found in nuts is much lower than would be found in potato chips or any breaded foods. There is no recommended maximum threshold that I’m aware of but if you are eating a normal Western diet the amount that you are going to get from a small handful of nuts is inconsequential. However, if you are concerned about this, you can just eat them raw or roast them at home where you can control the temperature and time.