A daily handful of walnuts can suppress hunger and make you feel full, according to new research.
The study shows that the nut contains high amounts of polyunsaturated fats (PUFAS) which prevent overeating.
Researchers say that is because they dampen down a hormone that boosts hunger, while firing up another that increases feelings of fullness.
Other foods rich in PUFAs include oily fish such as salmon and corn, grapeseed or canola oil.
These findings tell us that eating foods rich in PUFAs, like those found in walnuts, may favourably change appetite hormones so we can feel fuller for longer.
Professor Jamie Cooper
Nutritionist Professor Jamie Cooper, of the University of Georgia in the US, said: “Appetite hormones play an important role in regulating how much we eat.
“These findings tell us that eating foods rich in PUFAs, like those found in walnuts, may favourably change appetite hormones so we can feel fuller for longer.”
The study, published in the journal Nutrition, involved 26 young men and women aged 18 to 35 who had changes in hormone levels recorded as they were asked how hungry they felt.
The participants were placed on a seven day diet high in polyunsaturated fats consisting of a typical American eating pattern. Then they consumed meals high in saturated fat again.
Both diets contained the same number of total calories and percentage of fat – but the latter differed in the types.
Those that consumed a diet high in PUFAs had a significant decrease in fasting ghrelin, a hormone that increases hunger.
Meanwhile, there was a similar increase in peptide YY (PYY), a hormone that increases fullness or satiety.
Participants saw increases in PYY while fasting and after consuming a meal. These types of hormone changes imply better appetite control.
There was also no difference in responses to how hungry or full they felt and how much they thought they could eat – whether they ate the PUFA-rich diet, or not.
PUFAs are known to be good for health by helping reduce cholesterol and providing essential fats like omega-6 and omega-3 that the body can’t produce itself.
But the latest findings show for the first time how eating foods high in these polyunsaturated fats, consumers can curb overeating.
Through feedback, and by monitoring the hormone levels, the scientists were able to see the PUFA diet was more likely to leave consumers feeling full.
It included whole foods such as walnuts, Alaska salmon, tuna, flaxseed oil, grapeseed oil, canola oil and fish oil supplements. All meals were provided by the researchers.
The control diet was comprised of 7% polyunsaturated fat, 15% monounsaturated fat and 13% saturated fat, compared to the PUFA-rich diet which was 21% polyunsaturated fat, 9% monounsaturated fat, and 5% saturated fat.
Walnuts are unique among nuts because they are mainly comprised of PUFAs.
Every ounce – about seven whole walnuts – contains a remarkable 13 grams of PUFA out of 18 grams of total fat.
As a result they are the only nut to contain a significant amount of plant-based omega-3.
Prof Cooper, whose study was funded by the California Walnut Commission, added that larger and longer term studies are now required.
More clinical trials are also needed to determine the optimal intake of dietary PUFAs to offer the greatest health benefit.