Body weight gain results from an imbalance of energy intake and energy expenditure. High fat diets (more than 40% of energy from fat) have been reported to be a causative effect in the obesity crisis (1). There are three appetite hormones commonly studied following nutrient ingestion – ghrelin, peptide YY (PYY), and glucagon-like peptide-1 (GLP-1). Ghrelin, a hormone secreted by the stomach, have appetite-stimulating effects. PYY and GLP-1, hormones secreted by the small intestine and colon, have appetite-suppressing effects. Dietary manipulations that suppress ghrelin levels and increase PYY and GLP-1 levels may contribute to reducing energy intake (2).
A recent study found that consuming a high polyunsaturated fatty acids (PUFAs) diet may alter appetite hormones associated with hunger and satiety (3). The fatty acid profile was particularly high in alpha-linolenic acid (ALA). The clinical trial included 26 healthy, sedentary adults aged 18 to 35 years. Before the start of the intervention, the participants consumed a 3-day lead-in diet, representative of the average U.S. diet (providing 29%, 31% and 40% of energy at breakfast, lunch and dinner respectively). After the pre-diet, participants were divided into two groups and received either a PUFA rich diet (% energy from fatty acid – 21% PUFA including about 6.8% ALA, 5% saturated fatty acids [SFA] and 9% monounsaturated fatty acids [MUFA]) or a control diet (% energy from fatty acid – 7% PUFA, 13% SFA, 15% MUFA) for seven days. The control diet had the same macronutrient and fatty acid breakdown as the lead-in diet. PUFAs were provided by foods such as walnuts, salmon, tuna, flax seed oil, grapeseed oil and canola oil. The participants on the PUFA diet also consumed an additional 3g/d of combined eicosapentaenoic acid (EPA 2157 mg/day) and docosahexaenoic acid (DHA 843 mg/day).
After a 7 day period, fasting concentrations of ghrelin, PYY, insulin and leptin from pre- to post-diet intervention were assessed. The results showed that the PUFA rich diet led to a significant decrease in fasting ghrelin concentrations (a decrease in the range of 200 pg/ml compared to the pre PUFA rich diet) and a significant increase in fasting PYY concentrations (increase in the range of 30 pg/ml). There were no changes in fasting insulin or leptin (a satiety hormone release by adipose tissue), and no change in any fasting hormones for the control diet. The postprandial response to the high fat meals showed a significant greater PYY response after the 7 day PUFA-rich diet. They state “these findings show that the PUFA rich diet elicited greater physiological satiety through greater ghrelin suppression and higher PYY levels in healthy weight adults.”
In addition, a subjective visual analogue scale (VAS) was used to measure hunger and fullness. No changes in VAS were found. The results showed that consuming a PUFA-rich diet favourably alters some hunger and satiety hormone responses but does not significantly alter subjective rating of hunger or fullness. Combined with participants’ feedback, the researchers concluded higher PUFA levels were more likely to leave consumers feeling full.
PUFAs are essential dietary nutrients. However, public messaging arising in the 1980s led many consumers to believe that instead of replacing SFA with PUFA, fat should be avoided as much as possible. This caused a flood of low-fat foods on the market, which often were made more palatable with added sugars.
Satiety has been a major focus for food manufacturers, but the recent attention has been on protein. Early research pointed to PUFA for its effects on satiety (4), and though many scientists previously thought fat in general had a lower effect on satiety than other macronutrients, there is a growing body of research to suggest that PUFAs may be just as satiating as protein.
Science is supporting, and the food industry is recognizing, that it is the type of fat that is important. As a result, front of pack claims for ‘good fat’ such as omega-3 fatty acids are on the increase (5). This is good news for flaxseed!
References
- Stubbs RJ, Ritz P, Coward WA, et al. Am J Clin Nutr 1995;62:330-337.
- Cooper JA, Watras AC, Paton CM, et al. Appetite 2011;56:171-178.
- Stevenson JL, Clevenger HC, Cooper JA. Obesity (Silver Spring) 2015 Oct;23(10):1980-6. doi: 10.1002/oby.21202.
- Lawton CL, Delargy HJ, Brockman J, et al. Br J Nutr 2000;83:473-482.
- Mellentin, J. 2016. 10 Key Trends in Food, Nutrition & Health 2017. New Nutrition Business.