We all know that walnuts are good for us, but do you know why? There are a number of reasons for that, and this study (1) examined some of them in depth. 28 subjects with high body mass index, but without diabetes, were selected to test walnuts’ effect on the body. In particular, the test set out to determine why these nuts are associated with better metabolic health.
Two types of meals were selected for the participants: either a standard meal, or one that had walnuts incorporated. Macronutrients (Protein, Carbohydrate and Fat) for both were determined to be appropriately matched so there was as little variation as possible between them.
(Both types of meals involved the exciting combination of sugar-free jam and processed whole wheat bread. Because that’s not a meal anyone would get tired of really quickly…)
At the end of the study, they found that the group consuming the walnut meal had reduced post-meal insulin levels.
It should be noted, however, that the two meals tested were exactly the same, except that the walnuts were replaced with cream cheese in the second group.
Although the authors said that the two meals were equivalent, there’s actually a few key differences: walnuts contain 2.8 grams of fibre per serving, whereas cream cheese doesn’t contain any.
The second difference to to take note of is that we know that the protein present in cream cheese (which is high in branched chain amino acids) stimulates more insulin release.
Fatty Acids VS Saturated Fats
At the end of the study, the authors concluded that it was the types of fats between the two ingredient types that made the difference. Walnuts are primarily comprised of polyunsaturated fats, while cream cheese is in saturated fat-land.
The difference noted was related primarily to increased insulin release. We already know that butter—which is high in saturated fat—provokes almost no insulin release, so the lower insulin levels were most likely related to two other factors: increased fibre, and walnuts’ different amino acid profile.
Additionally, it’s interesting to note that those in the walnut group experienced an increase in glucagon after 120 minutes. This is something normally seen after higher-protein meals, which is also typically associated with more stable blood sugars.
In a way, glucagon acts in opposition to insulin, helping to bring extra energy out of storage. Insulin, on the other hand, is associated with fat storage and blocks fat burning.
The walnut meal contained both more fat, and more protein than the cream cheese meal. It’s known that this combination, with the addition of fibre, causes blood sugar stability for longer periods of time. This results in a lower insulin peak directly after a meal.
The conclusion?Walnuts are definitely good for our metabolisms, this is clear, but another food with a similar composition (like another type of nut) could likely provide the same benefits. It is also important to note that this study was funded by the California Walnut Commission. Additionally, fibre and certain types of amino acids will indeed affect insulin response after meals. Either way, we can see that eating walnuts or other nuts is definitely good for our metabolic health.
- Cheryl L. Rock*, Shirley W. Flatt, Hava-Shoshana Barkai, Bilge Pakiz, Dennis D. HeathA walnut-containing meal had similar effects on early satiety, CCK, and PYY, but attenuated the postprandial GLP-1 and insulin response compared to a nut-free control mealhttps://www.ncbi.nlm.nih.gov/pubmed/28610906