Relationship between adiposity and food intake: an example of pseudo-contradictory results obtained in case-control versus between-populations studies.

Seemingly contradictory data support controversies concerning the relationships between food intake and illnesses. The present study of 1035 adults, aged 30-39 years, shows that (1) daily energy intake is not higher in obese than in non-obese people, (2) obesity is more prevalent in social groups where energy intake is higher. These pseudo-contradictory results can be reconciled on the basis of a constitution/environment interaction. A comparison of groups based on presence or absence of illness (obesity, hypertension, coronary heart disease (CHD), cancer, etc) shows that some people can develop risk factors, even though their feeding behaviour is normal. This result (no direct relationship) underlines differences in individual susceptibility. When comparisons are made between populations with different diets the results (direct relationship) express environmental factors. The hypotheses on behavioural contribution to the aetiology of certain diseases appears more clearly in between-population comparisons than in case-control studies. Results of comparisons between populations (if the hypotheses they suggest are confirmed by intervention studies) warrant prevention at the level of populations, while results of case-control studies justify particular prevention in subjects at risk.