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Empty Calories - a real or imaginary problem? - November 2008
One of the more persistent beliefs about sugar is that it displaces vitamins and minerals from the diet. After all, it is argued, sugar is only calories: it contains no vitamins or minerals. So, obviously, any sugar in the diet must be at the expense of more useful foods that contain vitamins or minerals.
So, it comes as a surprise to many people, even experts in nutrition, to find repeated attempts to confirm this prejudice have failed to do so. Study after study has found that people who consume more sugar than average are just as likely to get enough of the essential vitamins and minerals (collectively called “micronutrients”) as people who avoid sugar (1). Certainly some people, including some children, do not seem to be consuming enough of a few of these micronutrients, but the amount of sugar they eat has virtually no relevance (2). The people who go short are those that either do not eat enough overall (if you do not eat you cannot take in the nutrients you need) or have strangely limited diets (3, 4). It is what you do not eat that determines your risk of micronutrient deficiency, not whether you have a sweet tooth. Surprisingly, most people who have enough to eat generally manage to include enough of all the micronutrients they need without thinking about their diets at all.
Indeed, sugar in the diet actually helps to make a wide variety of foods palatable, and it is variety that is the key to a healthy diet. Even among very young children, the amount of sugar they have in foods and drinks has been found to have virtually no influence on their micronutrient intake. This is surprising, since they tend to prefer more sugar than adults and have a smaller intake of food overall. So if anyone should show the expected shortfall in micronutrient intake it should be young children. In fact, most young children have adequate intakes of micronutrients, irrespective of their sugar intake. A few children who have a very high proportion of their food calories as sugar have a slightly lower micronutrient intake than those with average intakes of sugar. But this has little or nothing to do with how much sugar they prefer. It seems to be an illustration of a general rule that anyone who has an abnormally large proportion of their diet from one nutrient is likely to have an unbalanced diet that lacks something else. Those people with abnormally low intakes of sugar are just as likely to have low micronutrient intakes (5, 6, 7).
Sugar in the diet has a number of useful benefits that are often forgotten. In the first place, sugar is a carbohydrate, and therefore a useful part of this important contributor to a healthy diet (8). A second benefit is that people who eat more sugar tend to eat less fat (9). Since fat has the most important influence on body weight of all the nutrients, a lower fat intake usually means a lower risk of obesity (10, 11). And lastly, sugar helps to make many useful foods palatable that would otherwise be avoided, especially by children. It is this last benefit that probably accounts for the fact that people who eat more sugar than average rarely have inadequate micronutrient levels (3).
Eating too much of anything will lead to an unbalanced diet. But the evidence is clear that normal intakes of sugar have no appreciable adverse effects on the quality of the overall diet – and some benefits.
“Ah, but” we hear the cynics say “records of what people are eating are notoriously inaccurate, especially when it comes to foods and drinks they think they should not be having. So we cannot rely of these records to establish that sugar in the diet is not a problem”. In fact these records are quite sufficient to resolve this debate. Instead of grasping at straws to hang on to an old prejudice, we need to examine how food intake records are inaccurate and whether these errors will weaken the argument in favour of sugar’s innocence or strengthen it.
Certainly, there is ample evidence that dietary records frequently underestimate what some people are consuming (12). This has been inferred from the discrepancy between the total number of calories consumed when this is calculated from an individual’s food diary and the total estimated by a biochemical method called the “doubly labelled water method”. Many people’s food diaries give an estimate of total calorie intake that is appreciably less than the figure from the biochemical method. In fact, this error seems to be greater in people who are concerned about their food intake (so called “restrained eaters”) many of whom are overweight (13). But studies in which subjects were watched while they completed their food diaries have also shown that the error is caused by the subjects failing to report in their diaries when they eat or drink something that they feel will be disapproved of by the experimenters watching them. Among these items not reported are a number that contain sugar, such as confectionary bars or biscuits (14).
So food records are incomplete and our estimate of people’s nutrient intake is incomplete. Does this invalidate the conclusion that sugar has little or no influence on micronutrient intake? No, it does not, for several reasons.
If the food diaries are incomplete, then using them to estimate micronutrient intake will lead to a falsely low estimate of intake. It is impossible to gauge how much lower the estimate of micronutrient intake is than the true value without knowing precisely what foods are not accurately reported. But the key point is that any errors in food diaries will almost always lead to estimates of micronutrient intake that will be somewhat lower than their true value, not higher. As a result, the number of people, including children that are really consuming less vitamins or minerals than they need will be less than surveys suggest, not more.
Correspondingly, the estimate of sugar intake may also be lower than the true value. As a result, when researchers calculate the extent to which sugar intake influences micronutrient intake, they are comparing data that under-estimate micronutrient intake with data that under-estimate sugar intake. The consequence of these two errors will be that any graph showing a downward trend of micronutrient intake with increasing sugar intake that is based on these estimates is likely to be steeper than the true figures would give. Such a plot will tend to exaggerate the relationship. Or putting it another way, the true relation with sugar intake will be even less pronounced than the (inaccurate) estimates suggest. So since the estimates suggest any relationship is very weak and unlikely to be biologically (or practically) significant (1, 2, 3, 4), in reality, the idea that there is any link may be safely discarded.
References
For further information on empty calories please visit the Science Centre.
1. Food and Nutrition Board, Institute of Medicine, National Academy of Sciences (2002) Dietary reference intakes for energy, carbohydrates, fiber, fat, protein and amino acids. National Academic Press.USA
2. Forshee RA and Storey ML (2001) The role of added sugars in the diet quality of children and adolescents. Journal of the American College of Nutrition 20(1):32-43
3. Gibson SA (2007) Dietary sugars and micronutrient adequacy: a systematic review of the evidence. Nutrition Research Reviews 20:121-131
4. Rennie KL and Livingstone MBE (2007) Associations between dietary added sugar intake and micronutrient intake: a systematic review. British Journal of Nutrition 97:832-841
5. Gibson SA (1993) Consumption and sources of sugars in the diets of British schoolchildren: Are high-sugar diets inferior? Journal of Human Nutrition and Dietetics 6:355-371
6. Gibson SA (1997) Micronutrient intakes in British pre-school children: association with NMES. British Journal of Nutrition 78:367-378
7. Gibson, S. (2001) Dietary sugars and micronutrient dilution in normal adults aged 65 years and over. Public Health Nutrition 4:1235-1244
8. Food and Agriculture Organisation of the United Nations & World Health Organisation (1998) Carbohydrates in Human Nutrition. Report of a Joint FAO/WHO Expert Consultation. FAO Food & Nutrition Paper 66. http://www.fao.org/docrep/W8079E/W8079E00.htm
9. Hill JO and Prentice AM (1995) Sugar and bodyweight regulation. American Journal of Clinical Nutrition 62(suppl):245S-274S
10. Bray GA, Popkin BM (1998) Dietary fat intake does affect obesity! American Journal of Clinical Nutrition 68:1157-1173
11. Astrup A (2001) The role of dietary fat in the prevention and treatment of obesity. Efficacy and safety of low-fat diets. International Journal of Obesity 25(Suppl 1):S46-S50
12. Black AE, Cole TJ (2001) Biased over- or under-reporting is characteristic of individuals whether over time or by different assessment methods. Journal of the American Dietetic Association 101:70-80
13. Asbeck I, Mast M, Bierwag A, Westenhöfer J, Acheson KJ and Müller MJ (2002) Severe underreporting of energy intake in normal weight subjects: use of an appropriate standard and relation to restrained eating. Public Health Nutrition 5:683-690
14. Lafay L, Mennen L, Basdevant A, Charles MA, Borys JM, Eschwège E Romon M - The FLVS study group (2000) Does energy intake underreporting involve all kinds of food or only specific food items? Results from the Fleurbaix Laventie Ville Santé (FLVS) study. International Journal of Obesity 24:1500-1506
