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Sugar Wars, Episode 2: “Fructose Strikes Back”

Few food components have been demonized as much as fructose in the past decade. With fructose being presumed guilty in metabolic syndrome and heart disease, this systematic review sheds light on it’s actual impact on blood lipids.

Study under review: Effect of Fructose on Established Lipid Targets: A Systematic Review and Meta-Analysis of Controlled Feeding Trials

Introduction

Low-carb diets, saturated fat, and fructose: these constitute the holy trinity of hotly-debated topics in both the scientific literature and popular media. Luckily for us, when these disputes arise we often see an uptick in research as scientists try to fill in any knowledge gaps. In fact, 23 (39%) of the 59 trials included in the current meta-analysis on fructose were published within the past 15 years.

The deliberation over fructose has centered around what its metabolic effects may be, like its impact on diabetes risk or its role in the obesity epidemic. Dr. Robert Lustig has been a leading vocal proponent[1] of the fructose hypothesis[2], which contends that fructose plays a dominant role in the high rates of obesity, metabolic syndrome, type 2 diabetes, cardiovascular heart disease, non-alcoholic fatty liver disease, cancer, and poor lipid profiles. Dr. Lustig has also proposed fructose as a main mechanism in his “unifying hypothesis of metabolic syndrome[3]” and has drawn parallels between the negative health outcomes of chronic alcohol and fructose consumption[4]. His hypothesis has resonated with many. Dr. Lustig’s popular YouTube talk, Sugar: The Bitter Truth, has been viewed nearly six million times.

The concern over fructose has been echoed in public health guidelines provided by the American Heart Association[5] (AHA) and the Canadian Diabetes Association (CDA). The AHA has recommended limiting added sugars to 100 calories a day for women (about 34 grams) and 150 for men (about 51 grams), which is about 5% of daily calories. Their consensus statement also concluded that there were data indicating fructose intakes greater than 50-100 grams per day may elevate triglyceride levels. For reference (and as depicted in Figure 1), 50 grams of fructose would equate to about two 12 ounce cans of cola, 3.5 large red delicious apples, or seven cups of blueberries. The CDA has called for added sugars to make up no more than 10% of daily calories (50 grams on a 2,000 calorie diet) and that added fructose consumption above 60 grams a day may moderately increase triglycerides in people with type 2 diabetes. The CDA is careful to note that consuming naturally occurring fructose from fruit has not shown evidence of harm.

Figure 1: Fructose content of one cup (~150g) of fruits (and cola as a reference)

Source: USDA National Nutrient Database for Standard Reference Release 27.

The fructose hypothesis has been contested[6] by many scientists[7], including some of the authors[8] of the current paper. In the present review, Dr. John Sievenpiper and his team examine the effects of fructose on lipid targets, such as HDL, LDL, and triglycerides, for cardiovascular disease and metabolic syndrome. Two previous reviews on the effect of fructose on lipid profiles have been conducted. A 2008 review by Livesey and Taylor[9] indicated a ≥100 grams per day threshold, above which triglyceride levels were adversely affected. However, the review contained data from trials of both healthy and unhealthy participants, which may confound some of the findings. A second 2009 review[10] conducted by Sievenpiper et al. identified that a fructose intake greater than 60 grams per day in people with diabetes caused triglyceride levels to rise. Since then, 13 additional controlled fructose feeding trials have been conducted. The current review updates and expands on Sievenpiper’s previous paper.

Dr. Robert Lustig has proposed that fructose plays a primary role in causing obesity, type 2 diabetes, poor lipid profiles, and cardiovascular heart disease. The American Heart Association and the Canadian Diabetes Association have responded to these worries by proposing upper daily intakes of fructose. Many scientists disagree with the fructose hypothesis, including some of the authors of this review. This study aims to examine the effect that fructose may have on lipid profiles. Fifty-nine controlled feeding trials were examined for this analysis.

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