Sugar-fat seesaw: a systematic review of the evidence

Further to reports of a reciprocal relationship between sugar and fat intakes, this review aimed to provide an in-depth analysis and to determine the likely influence of this relationship on the achievement of population dietary guidelines. Using systematic methods, relevant literature was selected according to preset criteria. A strong and consistent inverse association was found between total sugars and total fat intakes expressed as percentage energy. Fewer studies considered absolute intakes and these reported a positive relationship, which may be influenced by confounding with energy intakes. Evidence for an inverse relationship between percentage energy from fat and extrinsic sugars was weaker and less consistent than for fat and total sugars. Reciprocal relationships were also observed for sugar-saturated fat, sugar-protein, sugar-alcohol, and sugar-starch expressed as percentage energy. Under-reporting of dietary intakes had no major influence on the findings. This review confirms the existence of the sugar-fat seesaw on a percentage energy basis and concludes that it is most likely explained by a combination of mathematical and food compositional effects. This finding is relevant because dietary guidelines are expressed as percentage energy and implies that at the population level multiple guidelines may be difficult to achieve in practice.