Research Updates | Obesity / Overweight
Choo, V.L. and co. reviewed the role of sugars in weight gain, overweight and obesity from high level evidence, systematic reviews and meta analyses of controlled dietary trials and prospective cohort studies.
Controlled dietary trials of the effect of chronic feeding with fructose-containing sugars and body weight can be categorised into the following 4 main trial designs:
1. Substitution trials in which added fructose containing sugars are compared with other macronutrient sources under energy-matched conditions
2. Addition trials in which fructose-containing sugars supplement a diet with excess energy compared with the same diet without the excess energy
3. Subtraction trials in which energy from fructose-containing sugars (usually in the form of sugar sweetened beverages (SSB)) is reduced by displacing it with water and/or non-caloric sweeteners or by eliminating it from the diet
4. Ad libitum trials in which energy from fructose-containing sugars is freely replaced with other sources of energy (usually starches or fat) without any strict control on the overall diet
Overall, substitution trials and addition trials indicate that fructose-containing sugars do not appear to behave differently from other sources of energy/macronutrients in contributing to weight gain. The subtraction trials in children failed to show weight loss and in adults there was modest weight loss. The ad libitum trials, the most reflective of real life, demonstrate that it is possible to lose weight following an ad lib diet high in fructose-containing sugars and there is no clear advantage for weight loss from replacing energy from fructose-containing sugars with other sources of energy e.g. fat, although there may be other health benefits of replacing with starchy foods that are higher in protein and fibre.
Prospective cohort studies comparing higher levels of SSB intake with the lowest have consistently shown an association between intake of SSB and body weight. Using energy-unadjusted models a significant positive association is seen, which implies that weight gain is mediated by energy and is more attributable to energy than to the SSB per se. Additionally, SSBs may be a marker of an unhealthy dietary and lifestyle pattern.
In conclusion, the evidence is not convincing that fructose-containing sugars contribute to weight gain, overweight and obesity more than any other source of energy/macronutrient. Sugars appear to increase body weight because they supply energy as opposed to any unique set of metabolic or endocrine mechanisms. Dietary pattern analysis shows the Western dietary pattern contributes to increased energy intakes and weight gain, as opposed to a specific role of any one component alone.
Longer terms studies (>12months) are needed to assess whether there are any potential adaptations that occur. More research is also needed to assess whether sugar in liquid vs. solid form may lead to greater weight gain over the longer-term under free-living conditions. A limitation of these studies is adiposity measures do not distinguish between fat mass and lean body mass.