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1 From the Clinical Nutrition and Risk Factor Modification Center (DJAJ, CWCK, and AM) and the Department of Medicine (DJAJ), St Michael’s Hospital, Toronto, and the Department of Nutritional Sciences, Faculty of Medicine, University of Toronto (DJAJ, CWCK, and AM).
2 Reprints not available. Address correspondence to DJA Jenkins, Clinical Nutrition and Risk Factor Modification Center, St Michael’s Hospital, 61 Queen Street East, Toronto, Ontario, Canada M5C 2T2. E-mail: cyril.kendall{at}utoronto.ca.
See corresponding article on page 774.
In this issue of the Journal, Gross et al (1) show that since 1963 carbohydrate intakes have increased by 126 g/d, with high-fructose corn syrup constituting 10% of total energy intakes. At the same time, the incidence of diabetes has increased by 47%. This important study highlights many key issues related to diet and lifestyle for the 21st century and beyond. Is the increased incidence of diabetes the result of an increased consumption of high-fructose corn syrup alone or of the consumption of the wrong type of carbohydrate in general? Or, does it reflect a total carbohydrate intake that is too high? Does this question belie the fact that we are now simply eating too much and exercising too little?
CARBOHYDRATE COMPARED WITH SUGAR
The panel that developed the dietary reference intakes established a low recommended dietary allowance for carbohydrate, 130 g (26% of a 2000-kcal diet), which is based on brain utilization and is in keeping with the trend established by the new dietary focus on carbohydrate restriction. Weight-loss diets in this category include the Atkins diet, which recommends carbohydrate intakes of <20 g/d during its induction phase. However, in view of the constraints imposed by other macronutrients, in terms of both health and the nature of the current food supply, another term was coined—the "acceptable macronutrient distribution range" (2). According to the acceptable macronutrient distribution range, 45-65% of total energy as carbohydrate is advocated. At this range, no upper level of sugar intake was established, but a maximum intake of 25% of energy was suggested. The article by Gross et al would have been useful as part of this debate.
Concerns about sugar being linked to concerns about refined carbohydrates in general are not new. These concerns have been expressed in the writings of Cleave (3), Yudkin (4), and Burkitt and Trowell (5). As the antithesis of fiber-rich foods, refined carbohydrates are linked to a wide array of chronic diseases, including colon cancer, diabetes, and cardiovascular disease. However, clear data on sugar consumption and specific diseases are not readily available. Fructose has been shown to raise serum triacylglycerol concentrations and possibly LDL-cholesterol concentrations (6), and refined carbohydrates may reduce circulating HDL-cholesterol concentrations. However, strong associations between sucrose and fructose intakes and heart disease or diabetes have not been shown, nor is there a clear indication that obesity is directly caused by increased sugar consumption or carbohydrate intake in general.
Furthermore, fructose—the major component of high-fructose corn syrup—has a low glycemic index, 20% that of glucose and 29% that of bread. Fructose has even been proposed as a carbohydrate source that may be of benefit in type 2 diabetes and at intakes of 60 g/d has been shown to lower hemoglobin A1c concentrations (7). However, the concern about the effects of fructose on serum triacylglycerol and HDL cholesterol remains (8).
EMPTY CALORIES
A further concern has been the lack of association between refined sugars and essential nutrients, vitamins, and minerals. In common with certain starchy foods, saturated fats, and alcohol, energy from refined sugars is considered to be "empty calories." As we prepare for a future of progressively reduced physical activity, the nutritional density, as opposed to nutrient density, ie, the consumption of essential nutrients per calorie, will have to increase so that requirements can be met at the lower caloric intakes necessitated by lower energy expenditure. Over the past decade, there has been concern about adequate intakes of vitamins and minerals, such as folate, thiamine, calcium, magnesium, and potassium. These concerns no longer relate to acute deficiency syndromes but to the long-term effects on health and the emergence of chronic diseases, including cardiovascular disease, certain cancers, osteoporosis, and hypertension.
REDUCED INTAKES OF TRADITIONAL STARCHY FOODS
Ironically, over the past 200 y or more, the increased consumption of refined-carbohydrate foods appears to have gone hand-in-hand with a reduced intake of traditional starchy foods, including truly whole-grain (pumpernickel) breads, cracked wheat (bulgur and tabouleh), dried peas, beans, and lentils. These foods are more slowly digested, have a lower glycemic index, and—in general—are more nutritionally replete than are their currently consumed counterparts (Table 1). Part of the reason for the increased consumption of refined carbohydrates may be that even starchy foods may taste sweet if they are rapidly digested by salivary amylase, which may contribute to the appeal of high-glycemic-index foods. Corn syrup and other sugars enhance the appeal of such foods. In this way, the glycemic load (glycemic index x total available carbohydrate) of the modern diet is likely to increase by a process of hedonic selection and overconsumption. High-glycemic-index and high-glycemic-load diets are associated with an increased risk of heart disease, diabetes, and certain cancers (9-13). Therefore, as we progressively eliminate traditional starchy foods from the diet, we may lose the protection that slow-release carbohydrate foods, such as pumpernickel bread, peas, beans, and lentils and their associated nutrients, provide against many major chronic diseases.
View this table:
TABLE 1. The glycemic index of some traditional and contemporary foods1
JUST TOO MUCH FOOD
Gross et al also note that, in the period since 1980, energy intakes have increased by 500 kcal/d. Data on physical activity were not available to these authors and, similarly, they had to rely on food disappearance data rather than on food intake data. These limitations did not diminish the authors’ hypothesis that increased calorie intakes contribute to obesity. In further support of their hypothesis, no data suggest that we are now exercising more at work or at play, but rather the reverse—we are becoming more sedentary. Furthermore, as noted by Gross et al, the dietary data were obtained over time in the same population. Thus, if we are in fact not eating more, we would have to postulate that we have also become wasteful over the past 2 decades. We need to add wastefulness to sloth and gluttony to categorize ourselves, for we are certainly becoming more obese.
Thus, the article by Gross et al raises many important issues. The most important of these issues is the increased consumption of highly processed, nutrient-depleted carbohydrate foods, especially those that contain high-fructose corn syrup as a key component. An increased consumption of these foods is associated with an increased incidence of type 2 diabetes, which itself is rising at an alarming rate. However, although high-fructose corn syrup is the focus of the article by Gross et al, perhaps the greatest value of their article is its emphasis on the quality of dietary carbohydrates and the questions it raises about the total amount of food consumed and the amount of energy expended. These concerns are a wake-up call for radical lifestyle reassessment. For the first time, exercise has become part of the dietary recommendations associated with the dietary reference intakes. One hour of moderate to vigorous exercise is recommended daily. If dramatic changes in exercise recommendations are required, what should we be doing about the food supply?
REFERENCES
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