The effect of two energy-restricted diets, a low-fructose diet versus a moderate natural fructose diet, on weight loss and metabolic syndrome parameters: a randomized controlled trial

Abstract

One of the proposed causes of obesity and metabolic syndrome is the excessive intake of products containing added sugars, in particular, fructose. Although the ability of excessive intake of fructose to induce metabolic syndrome is mounting, to date, no study has addressed whether a diet specifically lowering fructose but not total carbohydrates can reduce features of metabolic syndrome. A total of 131 patients were randomized to compare the short-term effects of 2 energy-restricted diets—a low-fructose diet vs a moderate natural fructose diet—on weight loss and metabolic syndrome parameters. Patients were randomized to receive 1500, 1800, or 2000 cal diets according to sex, age, and height. Because natural fructose might be differently absorbed compared with fructose from added sugars, we randomized obese subjects to either a low-fructose diet (<20 g/d) or a moderate-fructose diet with natural fruit supplements (50-70 g/d) and compared the effects of both diets on the primary outcome of weight loss in a 6-week follow-up period. Blood pressure, lipid profile, serum glucose, insulin resistance, uric acid, soluble intercellular adhesion molecule–1, and quality of life scores were included as secondary outcomes. One hundred two (78%) of the 131 participants were women, mean age was 38.8 ± 8.8 years, and the mean body mass index was 32.4 ± 4.5 kg/m². Each intervention diet was associated with significant weight loss compared with baseline. Weight loss was higher in the moderate natural fructose group (4.19 ± 0.30 kg) than the low-fructose group (2.83 ± 0.29 kg) (P = .0016). Compared with baseline, each intervention diet was associated with significant improvement in secondary outcomes. Reduction of energy and added fructose intake may represent an important therapeutic target to reduce the frequency of obesity and diabetes. For weight loss achievement, an energy-restricted moderate natural fructose diet was superior to a low-fructose diet.

Introduction

One of the proposed causes of obesity and metabolic syndrome is the excessive intake of products containing added sugars, in particular, fructose [1], [2], [3], [4], [5], [6], [7], [8], [9]. Fructose is a simple sugar that is present in honey and fruits; but the greatest source is from added sugars, such as table sugar (sucrose, a disaccharide of glucose and fructose) and high-fructose corn syrup (a mixture of free fructose and glucose usually in a 55:45 ratio). Experimental studies have shown that excessive concentrations of fructose (but not glucose) can induce all features of metabolic syndrome in rats [1], an effect that occurs independently of energy intake [1], [2], [3]. Clinical [4], [5], [6], [7] and epidemiologic [8], [9] studies also suggest that excessive fructose intake can cause metabolic syndrome. In particular, Stanhope et al [4] administered fructose to 34 healthy adults who subsequently developed postprandial hypertriglyceridemia, insulin resistance, and intraabdominal fat accumulation; these effects were not observed with glucose or starch-based diets. Similarly, in healthy subjects, fructose overconsumption has been associated with dyslipidemia and ectopic lipid deposition in liver and muscle [5]. In addition, Perez-Pozo et al [7] administered 200 g of fructose daily to healthy adult men and noted significant increases in ambulatory blood pressure, fasting serum triglycerides, weight, and insulin resistance (assessed by the homeostasis model assessment [HOMA]), with a significant decrease in high- density lipoprotein (HDL) cholesterol by 2 weeks [7]. Although the ability of excessive intake of fructose to induce metabolic syndrome in experimental animals and humans is mounting, to date, there is limited data regarding whether a diet specifically lowering fructose can reduce features of metabolic syndrome.

There is evidence to suggest that it is primarily the fructose content in added sugars that is important in promoting hypertension [10], possibly because natural fruits contain numerous beneficial substances, including antioxidants and flavonols. Because most diets that restrict fructose, such as low-carbohydrate–based diets, also reduce starches and high glycemic foods, we tested the hypothesis that a diet that specifically restricts fructose might reduce weight and features of metabolic syndrome in overweight and obese subjects. We further hypothesized that a diet in which the only source of fructose comes from natural fruits might be superior to one in which fruits consumption is limited. Therefore, we randomized participants to 2 energy-restricted diets, both of which excluded added sugars, a low-fructose diet allowing a limited consumption of fruits and a moderate-fructose diet in which natural fruits were allowed as the only source of fructose. We also included a modest caloric restriction in both diets, as this is the cornerstone of obesity management in clinical practice.