In search of flavour-nutrient learning. A study of the Samburu pastoralists of North-Central Kenya

Abstract

1Much of our dietary behaviour is learned. In particular, one suggestion is that 'flavour-2 nutrient learning' (F-NL) influences both choice and intake of food. F-NL occurs when an 3 association forms between the orosensory properties of a food and its postingestive effects. 4Unfortunately, this process has been difficult to evaluate because F-NL is rarely observed 5 in controlled studies of adult humans. One possibility is that we are disposed to F-NL. 6However, learning is compromised by exposure to a complex Western diet that includes a 7 wide range of energy-dense foods. To test this idea we explored evidence for F-NL in a 8 sample of semi-nomadic pastoralists who eat a very limited diet, and who are lean and food 9 stressed. Our Samburu participants (N= 68) consumed a sensory-matched portion (400g) 10 of either a novel low (0.72 kcal/g) or higher (1.57 kcal/g) energy-dense semi-solid food on 11 two training days, and an intermediate version on day 3. Before and after each meal we 12 measured appetite and assessed expected satiation and liking for the test food. We found 13 no evidence of F-NL. Nevertheless, self-reported measures were very consistent and, as 14 anticipated, expected satiation increased as the test food became familiar (expected-15 satiation drift). Surprisingly, we observed insensitivity to the effects of test-meal energy 16 density on measures of post-meal appetite. To explore this further we repeated a single 17 training day using participants (N= 52) from the UK. Unlike in the Samburu, the higher 18 energy-dense meal caused greater suppression of appetite. These observations expose 19 interesting cross-cultural differences in sensitivity to the energy content of food. More 20 generally, our work illustrates how measures can be translated to assess different 21 populations, highlighting the potential for further comparisons of this kind.

Modern ‘junk food’ and minimally-processed ‘natural food’ cafeteria diets alter the response to sweet taste but do not impair flavor-nutrient learning in rats

“…Ultimately both views would mean that new learning is rare but they make opposite claims about the status of flavor-nutrient associations in shaping motivation and food intake. It has recently been proposed that cross-cultural research can be valuable for these questions [79]. We also conclude from our present results that animal models can be improved by incorporating key features of the modern obesogenic environment and diet to better understand the roles that flavor-nutrient conditioning plays in environmentally-induced overeating.…”

Integration of Sweet Taste and Metabolism Determines Carbohydrate Reward

“…Third, in experiment 3 change in REE, but not change in liking, was correlated with NAc response, and change in liking was unrelated to change in REE. Collectively, these findings underscore the existence of separate mechanisms supporting the effects of conditioning on liking versus the neural representation of calorie predictive cues in the striatum, which is consistent with the distinctions draw between wanting and liking [44], and may explain the failure to observe robust flavor-nutrient learning in humans when explicit ratings of liking are measured [26, 28]. …”

Do humans still forage in an obesogenic environment? Mechanisms and implications for weight maintenance

“…flavour-nutrient learning over generations [70]. Consistent with this idea, peer modelling has been observed under controlled conditions [71] and can have a powerful effect on preferences in humans [72].…”