New research suggests that following a diet high in polyunsaturated fatty acids (PUFA), from foods like walnuts and salmon, may provide protection against the adverse effects of consuming meals high in saturated fats (SFA).1
Participants (26 healthy adults, ages 18-35) followed either a diet rich in PUFAs (21% polyunsaturated fat, 9% monounsaturated fat, and 5% saturated fat) or a control diet that was a typical American pattern (7% of polyunsaturated fat, 15% monounsaturated fat and 13% saturated fat) for seven days a meal high in SFA (7% of polyunsaturated fat, 16% monounsaturated fat and 47% saturated fat) both before and after the seven day diet. The diet rich in PUFAs was achieved by participants consuming walnuts, salmon, tuna, flaxseed oil, grapeseed oil, canola oil and fish oil supplements.
After consuming a PUFA-rich diet for one week, participants had improved fat metabolism and lower triglyceride levels. While improvements were seen for both men and women, women tended to benefit more from a PUFA-rich diet.
This study is the most recent publication from a clinical trial by researchers from the University of Georgia, all of which have shown potential benefits of regularly eating foods rich in PUFAs. The first study, published in 2016, found healthy adults who consumed the PUFA-rich diet for one week saw improved fat metabolism and lower cholesterol levels.2 The subsequent study, published in 2017, found that the PUFA-rich diet was associated with favorable changes in appetite hormones, including a significant decrease in fasting ghrelin (a hormone that increases hunger) as well as an increase in peptide YY (a hormone that increases fullness/satiety).3 The present paper further supports the adoption of a PUFA-rich diet for its potential metabolic benefits.
Walnuts are unique among nuts because they are primarily comprised of PUFAs, with 13 out of 18 grams of total fat per one ounce serving. As a result, they are the only nut to contain a significant amount of plant-based omega-3 ALA (2.5 grams per one ounce). Research on the health benefits of PUFAs continues to evolve and most recently the 2015-2020 Dietary Guidelines for Americans has recommended consuming this type of fat in place of saturated fat.
As with any research, there are important limitations to consider. Larger and longer-term studies, as well as studies in diverse populations, are needed to clarify population-wide effects. In the context of a whole food diet, such as the diet used in this study, it is difficult to discern whether changes can be attributed to one specific type of PUFA, food source, interactions between various hormones, or a combination of factors. Furthermore, participants consumed a relatively high percentage of PUFAs (21% out of the 35% of total energy from fat), which may not be feasible for the average adult. More clinical trials are needed to determine the optimal intake of dietary PUFAs that may offer the greatest benefit to appetite hormones and feelings of hunger and fullness, as well as exact mechanisms by which these occur.
Resources:
1 Kaviani S, Taylor CM, Stevenson JL, et al. A 7-day high-PUFA diet reduces angiopoietin-like protein 3 and 8 responses and postprandial triglyceride levels in healthy females but not males: a randomized control trial. BMC Nutrition. 2019;5:1. doi.org/10.1186/s40795-018-0262-7
2 Stevenson JL, Miller MK, Skillman HE, et al. A PUFA‑rich diet improves fat oxidation following saturated fat‑rich meal [published online ahead of print May 18, 2016]. Eur J Nutr. doi:10.1007/s00394-016-1226-9.
3 Stevenson JL, Paton CM, Cooper JA. Hunger and satiety responses to high-fat meals after high polyunsaturated fat diet: a randomized trial. Nutrition. doi: http://dx.doi.org/10.1016/j.nut.2017.03.008
