Food and Drug Reward: Overlapping Circuits in Human Obesity and Addiction
Written by Dr. Nora D. Volkow and colleagues. This paper describes the similarities between the mechanisms of obesity and addiction, with a focus on human brain imaging studies. Most researchers don't think obesity is an addiction per se, but the mechanisms (e.g., brain areas important for reward) do seem to overlap considerably. This paper is well composed and got a lot of media attention. Dr. Volkow is the director of the National Institute on Drug Abuse, a branch of the National Institutes of Health. The NIH is the main source of biomedical research funding in the US, and also conducts its own research.
Here's a quote from the paper:
There is now evidence that comparable dopaminergic responses are linked with food reward and that these mechanisms are also likely to play a role in excessive food consumption and obesity. It is well known that certain foods, particularly those rich in sugars and fat, are potently rewarding (Lenoir et al. 2007). High-calorie foods can promote over-eating (eating that is uncoupled from energetic needs) and trigger learned associations between the stimulus and the reward (conditioning). In evolutionary terms, this property of palatable foods used to be advantageous in environments where food sources were scarce and/or unreliable, because it ensured that food was eaten when available, enabling energy to be stored in the body (as fat) for future use. Unfortunately, in societies like ours, where food is plentiful and constantly available, this adaptation has become a liability.I think it's worth qualifying Dr. Volkow's statement that fat is highly rewarding. It definitely is-- in the context of a low-fat or typical diet. But in the context of a very high-fat diet, which is actually a reduced reward diet because it is restricted in carbohydrate, adding more fat does not increase the diet's reward value. In that context, carbohydrate will be more rewarding, whereas adding more carbohydrate to a high-carbohydrate diet will not increase its reward value. This is due to two factors: 1) carbohydrate and fat are both reward/palatability factors, and 2) food variety is a major reward/palatability factor (1). This is probably the main reason why monotonous liquid diets are so low in reward/palatability value: they eliminate variety. The main point I'm trying to make here is that I don't think fat is inherently fattening in humans-- it depends on the context.
Common Cellular and Molecular Mechanisms in Obesity and Drug Addiction
Written by Dr. Paul J. Kenny. This paper covers a similar topic to the one above, but with more of a focus on animal studies. Dr. Kenny is known for his work on D2 dopamine receptors in drug and food reward, and seems to be a growing authority in the field. This is a very nice, fairly technical, review of the neurological and molecular mechanisms involved in both processes. It was published in Nature Reviews Neuroscience, a high-profile science journal.
Is Fast Food Addictive?
Written by Drs. Andrea K. Garber and Robert H. Lustig. I don't know Dr. Garber, but Dr. Lustig is known for his strong anti-fructose advocacy. Dr. Lustig also believes that food reward/palatability contribute to obesity. This paper makes the case that fast food may act on reward pathways to such a degree that it can be addictive in susceptible people, and contribute to obesity and poor health.
Metabolic and Hedonic Drives in the Neural Control of Appetite: Who is the Boss?
Written by Dr. Hans-Rudolph Berthoud. Dr. Berthoud has been beating the reward-obesity drum for a long time now, and has written numerous review papers on the subject. I haven't read this one, but I've read two of his previous reviews and enjoyed them.