Nuts are packed with nutrients and fats that benefit heart and gut health. But those roasted at high heat, while tasty, can be risky.
Question:
I was interested to read about the gut-health benefits of peanuts and wondered if this finding applies equally to raw and unsalted roasted peanuts?
Answer:
Eating just 3-4 small handfuls of nuts a week can decrease the risk of coronary heart disease by about 20 per cent, according to the Heart Foundation. Moreover, recent research affirms that regular nut consumption promotes a healthy gut microbiome, which is beneficial.
However, when nuts are roasted, undesirable compounds can form. So, from a health perspective, is it best to avoid all roasted nuts?
The biggest issue with roasted nuts (particularly almonds) is the potential presence of acrylamide, a possible human carcinogen that has been found in animal studies to cause cancer.
We love the distinctive flavours that occur when nuts are cooked by high heat, but this can also produce acrylamide, which can form during the browning Maillard reaction between reducing sugars (glucose) and amino acids (asparagine) at temperatures above 120°C. How much forms depends on the cooking time and temperature, with higher temperatures and longer cooking times generally creating more.
However, several other foods contribute more acrylamide to our diet than roasted nuts. For New Zealand adults, potato products (hot chips, roast potatoes, crisps) are the most significant contributor, followed by bread (fresh or toasted), breakfast cereals and then beverages (beer, tea and coffee). When it comes to children, biscuits take that fourth spot in place of drinks.
From a nutrient perspective, roasted nuts will have varying levels of vitamins compared with raw nuts. For example, roasted almonds had more folate but significantly less vitamin B1 (thiamine) when assessed for the New Zealand Food Composition tables. It makes sense that roasting could cause the loss of heat-sensitive vitamins such as thiamine (folate is less sensitive to heat). But the problem with much of the data is that raw and roasted nuts do not necessarily come from the same batch, so slight nutrient differences may exist before they go through roasting.
However, there is more to nuts than just vitamins and minerals. Notably, they also provide a concentrated source of unsaturated fat and fibre. And it is likely the fibre, unsaturated fatty acids and polyphenols in nuts positively affect gut microbiota (the topic you were interested in), a 2020 review published in the journal Nutrients found. Both raw and roasted nuts sold in supermarkets have similar energy and fat profiles, according to a supermarket audit published in 2020. And a 2015 clinical study found roasting did not change the fat content of nuts. Most likely, light roasting will not significantly affect the fibre content either. So, whether nuts are roasted or not, you’ll probably improve your gut health by adding a regular handful to your diet.
Further, a randomised clinical trial published in the European Journal of Nutrition in 2017 found a light roasting did not appear to affect the cardioprotective effects of the raw nuts.
The Heart Foundation concluded that frequent nut consumption (3-4 servings of 15g a week) may reduce the risk of coronary heart disease by about 20 per cent. US researchers say nuts can lower the risk of other cardiovascular diseases by 13-19 per cent. These positive changes most likely occur by reducing nut eaters’ total cholesterol and LDL cholesterol levels.
To gain the best health benefits from nuts and nut butters, choose unprocessed nuts with no added salt, sugar or other fats. Or, lightly roast them yourself. Bake in a shallow dish in the oven at about 100°C to reduce acrylamide forming, occasionally stirring until the desired crunch is reached.
And as the Heart Foundation wisely notes, if those lightly roasted nuts replace less-nutritious snacks such as potato chips or biscuits, they will likely provide more health benefits. So, enjoy those tasty nuts, raw or lightly toasted.
