While rates of global obesity are high, a substantial proportion of the population remain lean despite living in an obesogenic environment. One potential difference between obesity resistant individuals (ORIs) and obesity susceptible individuals (OSIs) is oral fatty acid sensitivity. We compared oral fatty acid sensitivity and fat ranking ability between ORIs and OSIs. Oral sensitivity to oleic acid (1.4 mM) was determined using triplicate triangle tests amongst 50 ORIs and 36 OSIs. Participants tasted three milk samples, consisting of one sample with oleic acid and two control samples without oleic acid. Hypersensitive individuals were defined as those who chose the oleic acid sample three out of three tests. Participants also ranked the fat content of custard samples containing 0%, 2%, 6% and 10% fat. Logistic regression models including sex, age, and percentage body fat estimated adjusted odds ratios (OR) for oral fatty acid sensitivity between ORI and OSI. Negative binomial regression adjusting for age, BMI, and height compared fat ranking scores between ORIs and OSIs. The odds of being hypersensitive to fatty acids amongst ORIs was 3.60 times that for OSIs (P=0.034). There was no evidence for an association between resistance to obesity and the ability to rank the fat levels in a food (P=0.600). Hypersensitivity to oral fatty acids among ORIs may influence their dietary fat intake, and thus their body weight regulation. Future larger studies are needed to confirm this.

The rapid rise in obesity in recent decades is of great concern due to the associated co-morbidities and subsequent strain on healthcare. Of interest are those who remain lean despite living in an obesogenic environment. Investigating the characteristics of these seemingly obesity resistant individuals may allow us to identify important factors to prevent and treat obesity. Although it is well known that the causes of obesity are complex and multi-factorial, the excessive intake of calories, including fat, is a key problem. Previous research has reported oral hypersensitivity to fat is associated with lower energy and fat intakes, BMI, and waist circumference. It is purported that this may be due to the fact that high fat foods are less preferred and therefore eaten less frequently among sensitive individuals. This hypersensitivity may enhance preference for lower energy-dense foods and may be one mechanism whereby obesity resistant individuals (ORIs) regulate their energy intakes. Indeed it has been reported that obesity susceptible individuals (OSIs) are characterised by strong preference for palatable foods, particularly high fat foods. However, it is yet to be determined whether individuals may be predisposed to obesity on the basis of being relatively insensitive to oral fatty acids or, alternatively, whether individuals may be protected against obesity by having a heightened sensitivity to oral fatty acids. Therefore the aim of this study was to compare fatty acid sensitivity and fat ranking ability between those who are resistant and susceptible to obesity.

The six item instrument for screening ORI and OSI was completed by 172 participants as part of the recruitment phase (further details of these participants not shown here). The Cronbach alpha, after reverse coding the two ORI items, showed good internal consistency (alpha 0.86; 95% CI: 0.83, 0.88; lowest itemrest correlation 0.45) with only a very small improvement possible by removing an item (ORI item 3: I am a person who loses weight easily, alpha increased to 0.87). This provides support for the construct validity of the instrument in this population, alongside its face and content validity. Despite our results on fat sensitivity, there was no evidence for ORIs to be better at ranking fat levels in a common food, namely custard. If indeed our ORIs, who appear more sensitive to fat, have reduced preference for high fat foods, their ability to detect different fat levels remains unclear. Further studies should assess the fat ranking ability of ORIs, using a number of different foods. Future research could investigate the effects of changing fat sensitivity amongst those prone to obesity. Previously Stewart et al. showed consumption of a low fat diet for four weeks increased fatty acid sensitivity among both lean and overweight participants suggesting that sensitivity can indeed be recalibrated. The long-term maintenance of such recalibrations would be important for interventions using this to improve weight management. Overall it appears that those individuals resistant to obesity are more likely to be sensitive to dietary fat, which may be one mechanism whereby obesity resistant individuals remain lean despite living in an obesogenic environment.

Warm Regards,
Joseph Kent
Journal Manager
Journal of Clinical Nutrition & Dietetics