Time of day influences relative glycaemic effect of foods

Nutrition Research, Vol. 16, No. 3, pp. 381-384, 1996 Copyright Q 1996 Elsevier Science Inc. Printed in the USA. All rights reserved 0271.5317/96 $15.00 + .oO ELSEVIER

PI1 SO271-5317(96)00019-X

TIME OF DAY INFLUENCES

RELATIVE

GLYCAEMIC

EFFECT

OF FOODS

Thomas MS Wolever, DM, PhD, and Claudia Bolognesi, BSc. Department of Nutritional Sciences, and Clinical Nutrition and Risk Factor Modification Centre, St. Michael’s Hospital, University of Toronto, Toronto, Ontario, Canada.

ABSTRACT

To see if time of day affected the relative glycaemic effect of foods, we studied 8 non-diabetic subjects in random order on 4 days over a 2-week period. They were given 5Og carbohydrate portions of corn or oat-psyllium cereal plus 200ml2% milk. Each test meal was taken either at 08:OOh after a lo-12h overnight fast, or at 12:00h, 3.5h after a standard breakfast. The incremental area under the glycaemic response curve for corn cereal taken at breakfast was greater than that at lunch, 103~1~13 versus 52*6 mmolmin/L (p
INTRODUCTION

The glycaemic responses of equal carbohydrate portions of different starchy foods, classified by the glycaemic index (GI), vary over a 3- to 4-fold range (1,2). The differences are believed to be due, at least in part, to differences in the rates at which foods are digested and absorbed from the gastrointestinal tract (3). The role of the GI in clinical practise is controversial, but it is generally agreed that the principle may be useful and that more research is needed (4). The GI of foods is usually determined by tests conducted in the morning after an overnight fast (5). However, some investigators feed test meals at lunch time (6,7). It is not known if time of day affects the relative glycaemic responses of foods. Thus, the objective of this preliminary study was to see if the relative glycaemic effects of two foods were the same when tested at breakfast or lunch time.

Address for correspondence: Dr. Thomas MS Wolever, Associate Professor, Department of Nutritional Sciences, University of Toronto, Toronto, Ontario, Canada M5S lA8. 381

382

T.M.S. WOLEVER and C. BOLOGNESI

MATERIALS

AND METHODS

Non-diabetic subjects (4 male, 4 female; age 25.6kO.7 yr; BMI 24.Okl.2 kg/m’) were studied on 4 days in random order over a a-week period using a protocol approved by the University of Toronto Human Subjects Review Committee. They were given test meals consisting of 59g corn cereal or 82g oat-psyllium cereal (Kellogg Co., Battle Creek, MI) plus 2OOml2% milk. The test meals, containing 60g available carbohydrate (5Og from cereal and log from milk), were served with 250ml tea or coffee plus 3Oml2% milk as desired (drink standard for each subject) and eaten within 1Omin. In separate tests, the GI of corn cereal was 124h15 (n=7), similar to that for cornflakes, 121 (5), and the GI of oatpsyllium cereal was 61*8 (n=13). The test meals were eaten either at 08:OOh(breakfast) after a lo-12h overnight fast, or at 12:OOh(lunch). For the first lunch test, subjects came to the laboratory at S:OOam, ate a breakfast of as much bread, butter, jam and tea or coffee as desired (mean*SEM intakes: energy 3680*49OkJ, 152+23g carbohydrate and 16&2g fat), and were asked not to do any strenous physical activity before lunch. On the second lunch test day, subjects ate the same breakfast and did the same activity as on the first day. Finger-prick blood samples (=2OOpL) were taken into fluoro-citrate tubes before, and at 15, 30,45, 60 and 90 min after starting to eat, placed on ice immediately, then kept at -20°C for a maximum of 24h before analysis of whole blood glucose using an automatic analyser (Model 2300 STAT, Yellow Springs Instruments, OH). Results are expressed as means*SEM. Incremental areas under the curve ignoring area below the baseline (AUC) were calculated as previously described, (5). Data were subjected to analysis of variance examining for the main effects of time of day (ie. breakfast vs lunch) and test meal.

RESULTS

The glycaemic responses after the 4 test meals are shown in Figure 1. The AUC for corn cereal at breakfast and lunch and oat-psyllium cereal at breakfast and lunch, respectively, were 103+13,52+12,52+6 and 41fll mmolmin/L. The mean AUC at breakfast was significantly greater than at lunch (p
DISCUSSION

The results are similar to some previous studies in non-diabetic subjects which show that glycaemic responses at lunch are less than those at breakfast (8). However, this is not

383

DIET AND GLUCOSE

i2F

q@@

09:oo

13:oo

Time of Day (hrs)

FIGURE 1 Blood glucose responses after corn (0) and oat-psyllium (0) cereals taken at 08:OOh after a lo-12h fast (left> or at noon after a standard breakfast (right). Values are mean&EM.

a universal finding, and glycaemic responses at lunch depend upon many factors including the nature of both the breakfast and the lunch meals (9,10,11). The glycaemic responses at breakfast were also less variable than those at lunch. Thus, to determine the glycaemic effects of foods, more reliable results may be able to be obtained by doing the experiments in the morning after an overnight fast rather than at mid-day after a standard breakfast. The difference between the glycaemic responses of the 2 cereals taken at breakfast, 50%, was almost identical to the 47% difference predicted by the glycaemic index, but the difference between the same cereals tested at lunch-time was only 2 1%. This is consistent with previous studies in both non-diabetic (12) and diabetic (13) subjects showing no difference between the lunch-tune glycaemic responses of low- versus high-glycaemic index diets. Nevertheless, low-glycaemic index diets reduce postprandial blood glucose at breakfast and dinner and reduce serum glycosylated albumin or HbAlc (12,13). Thus, the lack of the expected reduction in blood glucose at lunch does not invalidate the clinical utility of the glycaemic index. Indeed, at least 3 different groups have shown that a low glycaemic index diet improves blood glucose control in diabetic subjects (5). The effect of tune of day on relative glycaemic responses may depend upon the nature and composition of the previous meal. Further studies are needed to determine the mechanism for this effect and to see if it occurs in diabetic subjects. However, these results have potential implications for the interpretation of studies in which glycaemic responses were measured at lunch time, and also may be relevant to persons with diabetes who use home blood glucose monitoring.

ACKNOWLEDGEMENTS

Supported by the Natural Sciences and Engineering Research Council of Canada, and Kellogg Canada Inc. CB was supported by a Rotary International Scholarship.

T.M.S.

384

WOLEVER

and C. BOLOGNESI

REFERENCES

1) Jenkins DJA, Wolever TMS, Taylor RH, Barker HM, Fielden H, Baldwin JM, Bowling AC, Newman HC, Jenkins AL, Goff DV. Glycemic index of foods: a physiological basis for carbohydrate exchange. Am J Clin Nutr 1981;34:362-66. 2) Wolever TMS, Katzman-Relle L, Jenkins AL, Vuksan V, Josse RG, Jenkins DJA. Glycaemic index of 102 complex carbohydrate foods in patients with diabetes. Nutr Res 1994; 14:65 l-69. 3) Jenkins DJA, Ghafari H, Wolever TMS, Taylor RH, Barker HM, Fielden H, Jenkins AL, Bowling AC: Relationship between the rate of digestion of foods and postprandial glycaemia. Diabetologia 1982;22:450-55. 4) American Diabetes Association Policy Statement. Glycemic effects of carbohydrates. Care 1984;7:607-8.

Diabetes

5) Wolever TMS, Jenkins DJA, Jenkins AL, Josse RG. The glycemic index: methodology and clinical implications. Am J Clin Nutr 1991;54:846-54. 6) Coulston AM, Hollenbeck CB, Swislocki ALM, Reaven GM. Effect of source of dietary carbohydrate on plasma glucose and insulin responses to mixed meals in subjects with NIDDM. Diabetes Care 1987;10:395-400. 7) van Amelsvoort JMM, van Stratum P, Dubbelman GP, Lussenburg RN. Effects of meal size reduction on postprandial variables in male volunteers. Ann Nutr Metab 1990:34: 163-74. 8) Genuth SM. Plasma insulin and glucose profiles in normal, obese and diabetic persons. Ann Int Med 1973;79:812-22. 9) Service FJ, Hall LD, Westland RE, O’Brien PC, Go VLW, Haymond MW, Rizza RA: Effects of size, time of day and sequence of meal ingestion on carbohydrate tolerance in normal subjects. Diabetologia 1983;25:3 16-21. 10) Collier GR, Wolever TMS, Jenkins DJA. Concurrent ingestion of fat and reduction in starch content impairs carbohydrate tolerance to subsequent meals. Am J Clin Nutr 1987;45:963-69. 11) Jenkins DJA, Wolever TMS, Taylor RH, Griffiths C, Krzeminska K, Lawrie JA, Bennett CM, Goff DV, Sarson DL, Bloom SR: Slow release carbohydrate improves second meal tolerance. Am J Clin Nutr 1982;35:1339-46. 12) Jenkins DJA, Wolever TMS, Collier GR, Ocana A, Rao AV, Buckley G, Lam KY, Meyer A, Thompson LU: The metabolic effects of a low glycemic index diet. Am J Clin Nutr 1987;46: 968-75. 13) Brand JC, Colagiuri S, Crossman S, Allen A, Truswell AS: Low glycemic index carbohydrate foods improve glucose control in non-insulin dependent diabetes mellitus (NIDDM). Diabetes Care 1991;14:95-101. Accepted

for

publication

August

21,

1995.