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

Abstract

Animals learn to prefer and increase consumption of flavors paired with postingestive nutrient sensing. Analogous effects have been difficult to observe in human studies. One possibility is experience with the modern, processed diet impairs learning. Food processing manipulates flavor, texture, sweetness, and nutrition, obscuring ordinary correspondences between sensory cues and postingestive consequences. Over time, a diet of these processed 'junk' foods may impair flavor-nutrient learning. This 'flavor-confusion' hypothesis was tested by providing rats long-term exposure to cafeteria diets of unusual breadth (2 or 3 foods per day, 96 different foods over 3 months, plus ad libitum chow). One group was fed processed foods (PF) with added sugars/fats and manipulated flavors, to mimic the sensory-nutrient properties of the modern processed diet. Another group was fed only 'natural' foods (NF) meaning minimally-processed foods without manipulated flavors or added sugars/fats (e.g., fresh fruits, vegetables, whole grains) ostensibly preserving the ordinary correspondence between flavors and nutrition. A CON group was fed chow only. In subsequent tests of flavor-nutrient learning, PF and NF rats consistently acquired strong preferences for novel nutrient-paired flavors and PF rats exhibited enhanced learned acceptance, contradicting the 'flavor-confusion' hypothesis. An unexpected finding was PF and NF diets both caused lasting reduction in ad lib sweet solution intake. Groups did not differ in reinforcing value of sugar in a progressive ratio task. In lick microstructure analysis the NF group paradoxically showed increased sucrose palatability relative to PF and CON, suggesting the diets have different effects on sweet taste evaluation.

Cafeteria diet decreases sucrose preference and increases the sensitivity of risperidone in the caloric intake of Wistar rats

“…An increase in abdominal fat is a risk factor for the development of other comorbidities and metabolic changes associated with obesity, such as Type 2 diabetes mellitus, dyslipidemia, cardiovascular diseases such as atherosclerosis and acute myocardial infarction (Gonz alez-Muniesa et al, 2017;Romieu et al, 2017) In rodents, a low responsiveness to the reward stimulus can be understood as a state of anhedonia (Liu et al, 2018;Garcia-Carachure et al, 2020). Other studies have already performed the sucrose preference test in animals on a cafeteria diet to check the anecdotal status, finding no differences (Macedo et al, 2015) or reporting low preference of these animals compared to the Control group (Gac et al, 2015;Martire et al, 2015;Palframan and Myers, 2016). Anhedonia-like behavior has also been associated with the development of binge eating and consequently obesity (Coccurello, 2019;Keating et al, 2019;Moreira et al, 2019), which is in line with the results found with the Cafeteria group in the present study.…”

The role of low-calorie sweeteners in the prevention and management of overweight and obesity: evidence v. conjecture

“…The finding that rats fed glucose-sweetened yoghurt gained more weight is plausibly explained by a lack of full compensation for the higher energy content of the glucose-sweetened yoghurt ( 29 ) . Relatedly, another recent study found that exposing rats to a large variety of highly processed foods did not impair flavour-nutrient learning, compared with exposure to either a variety of minimally processed foods or a standard chow diet ( 32 ) . The authors conclude that their results contradict the flavour-confusion hypothesis.…”

Promoting healthy food preferences from the start: a narrative review of food preference learning from the prenatal period through early childhood

“…Relatedly, one study compared the effects of chronic consumption (from pre‐puberty into young adulthood) of a highly processed, ‘junk food’ diet versus an equally diverse but ‘natural’ diet of minimally processed whole foods (fruits and vegetables, whole grains, lean meats, etc. without added fats, sugars or flavours) . The ‘junk food’ diet was selected to mimic modern diets high in processed foods and included a wide variety of packaged foods with added sugars, fats and flavours, such as pastries, sugary breakfast cereals and ready‐to‐eat microwavable pasta.…”