A Simopoulos and J DiNicolantonio (2016) Clin Psychol Rev. Open Heart 2016; 3(2) e000385 Published online 2016 Sep 20 doi: 10.1136/openhrt-2015-000385 PMCID: PMC5093368 PMID: 27843563
In the United States, the weight associated with the greatest longevity tends to be below the average weight of the population under consideration, if such weights are not associated with a history of significant medical impairment. Overweight persons tend to die sooner than average-weight persons, especially those who are overweight at younger ages. The effect of being overweight on mortality is delayed and may not be seen in short-term studies. Cigarette smoking is a potential confounder of the relationship between obesity and mortality. Studies on body weight, morbidity, and mortality must be interpreted with careful attention to the definitions of obesity or relative weight used, preexisting morbid conditions, the length of follow-up, and confounders in the analysis. The terminology of body weight standards should be defined more precisely and cited appropriately. An appropriate database relating body weight by sex, age, and possibly frame size to morbidity and mortality should be developed to permit the preparation of reference tables for defining the desirable range of body weight based on morbidity and mortality statistics.1
Based on body mass index (BMI), 1.5 billion people are overweight (BMI≥25.0 kg/m2) and 500 million of them are classified as obese (BMI≥30 kg/m2).2–3 Since 1980 there have been many studies on the causes and management of obesity including behavioural studies, physical activity studies, nutritional studies ranging from high-protein low-carbohydrate low-fat, high-carbohydrate low-calorie diets and drugs for the treatment of obesity, yet despite all these efforts the US population continues to increase its weight and similar situations exist in other countries, both developed and developing. In developing countries, obesity coexists with undernourished and malnourished individuals. So far, no country has been able to either prevent overweight and obesity or maintain weight loss of its population.
International organisations and many scientists continue to consider obesity the result of an imbalance between energy intake and expenditure. Citing the law of thermodynamics, scientists and industries articulated the concept of ‘a calorie is a calorie’, which led to the development of a huge weight loss industry, various diets substituting ‘calories for other calories’ and books promoting ‘eat less and exercise more’. These approaches continue to be espoused today, despite the scientific evidence that ‘a calorie is not a calorie’, and that the sources of calories are important in influencing human metabolism and appetite control.4–6 For example, calories from vegetable oils high in linoleic acid (LA), an ω-6 fatty acid, are proinflammatory and thrombogenic, whereas calories from eating fish high in ω-3 fatty acids are anti-inflammatory and antithrombotic. High ω-6 fatty acid intake increases white adipose tissue that is stored and prevents its browning.7 8 Furthermore, calories from ω-6 fatty acid intake from vegetable oils high in LA (corn oil, sunflower, safflower, cottonseed, soya bean oil) have different effects on fat tissue development and type than calories from ω-3 fatty acid intake high in α-linolenic acid (ALA) (such as flaxseed oil, canola oil, perilla oil, chia oil). In addition, high ω-6 fatty acid intake leads to an inflammatory state, which is at the basis of obesity and other chronic diseases, whereas calories from ω-3 fatty acids have the opposite effect9 10 (box 1 and table 1). ω-6 and ω-3 fatty acids are essential for health and must be obtained from the diet by all mammals including human beings.