The Australian dietary guidelines recommend that we eat 30 grams (one ounce) of nuts every day – a handful. But many of us know that nuts are rich in calories and fat.
So should we eat nuts or will they let us arrive?
In short, the answer is yes, we should eat them, and no, they will not make us arrive when they are eaten in moderate quantities. The fats in nuts are usually the “good” fats. And apart from that our bodies do not absorb all the fat found in nuts. But we do absorb the nutrients that they supply.
Dietary fat: friend or foe?
Nuts do contain fat and the amount of fat varies between the nut types. For example, a portion of raw cashew nuts or pistachios of 30 grams contains about 15 grams of fat, while the same amount of raw macadamia contains about 22 grams of fat.
There are different types of fats in our diet and some are better for us than others. Nuts mainly contain monounsaturated and polyunsaturated fats. These types of fats are known as “good fats.” They can help lower cholesterol when we eat them instead of saturated fats.
The type of fats present varies between notes. For example, walnuts are rich in polyunsaturated fats, while other types of nuts, such as hazelnuts and macadamia, contain more monounsaturated fat.
What the evidence says
Even if the type of fat in nuts is good for us, they still contain a lot of fat and calories. But this does not mean that we must avoid them in order to control our weight.
Studies that looked at the eating habits and body weight of people over a long period of time have shown that people who regularly eat nuts get less weight over time than people who do not.
We see a similar pattern in clinical studies in which people were asked to include nuts in their diet and then looked at their effects on body weight.
An overview of more than 30 studies examined the effects of eating nuts on body weight. It did not find people who ate nuts increased their body weight, body mass index (BMI) or waist circumference, compared with a control group of people who did not eat nuts.
In fact, a study discovered that when people ate a pattern of food that focused on weight loss, the group of people who ate nuts lost more body fat than those who did not eat nuts.
Let’s nut this out
There are several possible explanations why eating nuts does not seem to lead to weight gain.
We do not absorb all the fat in nuts: the fat in nuts is stored in the cell walls of the nut, which do not easily break down during digestion. As a result, if we eat nuts, we do not take all the fat. Part of the fat is passed on in our feces. The amount of calories we absorb by eating nuts can be between 5 and 30 percent less than we had previously thought.
Nuts increase the amount of calories we burn: not only do we absorb all the calories in nuts, but eating nuts can also increase the amount of energy and fat that we burn. This is thought to be partly explained by the protein and unsaturated fats in nuts, although we do not yet know exactly how this happens. Increasing the number of calories burned can help us to maintain or lose weight.
Nuts help us stay full longer: in addition to fat, nuts are rich in protein and fiber. So, nuts help keep us feeling full after we have eaten them, which means we are probably eating less at later meals. Recent studies have also suggested that people provide nuts to improve the overall quality of the types of food they eat. This may be because nuts replace “junk food” as snacks.
People who eat nuts have a healthier lifestyle in general: we can not exclude that eating nuts is only a sign of a healthier lifestyle. However, randomized controlled trials, which can control lifestyle factors such as eating habits, still do not have a negative effect on body weight when people eat nuts. This means that the beneficial effects of nuts are not only the result of nut eaters who have healthier lifestyles – the notes themselves play a role.
Generally, evidence suggests that nuts are a healthy snack that can provide us with many nutrients that our body needs. We can confidently include the recommended 30 grams of nuts per day in a healthy diet without worrying about the effect they will have on our waistlines.
Elizabeth Neale is a career development employee at the University of Wollongong; Sze-Yen Tan is Senior Lecturer in Nutritional Sciences at the Institute for Physical Activity and Nutrition (IPAN), School of Exercise and Nutrition Sciences, Deakin University; Yasmine Probst is an associate professor at the School of Medicine, University of Wollongong.