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mccoy

Exercise and glucose peaks-AUC

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Effect of exercise timing on elevated postprandial glucose levels

A very interesting article on a study carried out on healthy people. The results are not what I expected. A continuos glucose meter was applied to a control group and to other 3 groups, one exercising before meals, the other exercising after meals, the third one doing small bouts of exercise tthruout the day. The latter turned out to be the more effective in keeping AUC lower. Exercise just after meals lowers the peak but later causes a higher rebound. CON is the reference curve, the control group. Incredibly, postprandial exercise causes delayed but significantly higher peaks.Brief periodic exercise appears to be very effective.
 
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This is the temporal distribution of exercise:
 
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Also, there appears to have been no statistical significant difference in AUC for all groups, even though the average is lower in brief exercise.
 
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This is another interesting article

Postprandial glucose fluxes and insulin sensitivity during exercise: A study in healthy individuals

12 healthy individuals carried out exercise at 50% VO2 max after lunch. Their average fasting glucose was 85 mg/dl. The curves are interesting to view. Exercise, after 120 minutes from meal, drastically lowered BG as foreseeable. Then endogenous glucose production prevents hypoglicemia with an increasing trend until end of exercise, were baseline was reached again at 240 minutes from meal. Insuline is a good proxy for BG, until exercise starts. Glucagon as expected lowers after meal but rises during exercise, since its function is to trigger endogenous glucose release in the liver.

Interestingly, I myself observed a similar decrease of minus 40 mg/dL after 20-30 minutes of similar exercise (moderate speed on the threadmill).

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Edited by mccoy

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The beneficial effects of endurance training on plasma glucose concentration are well illustrated in this recent article.

Measurement of postprandial glucose fluxes in response to acute and chronic endurance exercise in healthy humans

The curves depict the results of a mixed meal tolerance test without exercise, 21 hours after and intense bout and after a 4 weeks chronical exposure to endurance exercise. Also triglycerides and insulin are reported.

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Edited by mccoy

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Yet another very interesting study showing that 5  days overfeeding does not alter  glycemic tolerance (maybe improves it) and 28 days overfeeding alters it but not hugely, providing that the nutrient ratios are kept constant.

In the discussion it is reported that if the caloric surplus is provided by fat, glucose homeostasis is altered and tolerance to glucose decreases, as a response to increased fat metabolism (as shown in different studies). Takehome lesson is maybe that if we'd like to eat more to increase bodyweight or as as a response to exercise we'd better increase proportionally fat and carbs, not just fat. Or maybe overfeed in cycles of 5 days.

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An important finding of the present study was that fasting glucose was unaltered by overfeeding, and postprandial glycemia was only modestly increased by chronic, but unchanged by short-term, overfeeding. This is in contrast to a range of previous data in humans demonstrating that overfeeding for 3–7 days increases fasting (10, 12, 13, 22, 34) and postprandial (22, 34) glycemia in healthy humans. However, the majority of these overfeeding studies utilized diets that substantially increased the relative amount of energy derived from fat (10, 12, 22, 34). Indeed, following only 7 days of overfeeding a diet containing 60% energy from fat (increased from 31.5% in the habitual diet), Parry et al. (34) recently demonstrated similar increases in postprandial glucose AUC and insulin AUC during a meal tolerance test as in the current chronic overfeeding study. Thus, 7 days of high-fat overfeeding has a similar impact on postprandial glucose and insulin as 28 days of overfeeding with a mixed macronutrient composition. Although some studies utilizing habitual macronutrient compositions or high-carbohydrate overfeeding diets have demonstrated significant alterations to fasting or postprandial glycemia in the short term (13), the changes are typically much smaller than those from diets utilizing a high fat composition (1, 28). Thus, overfeeding with a diet that increases the proportion of dietary fat may bias toward an impairment in glucoregulatory function by increasing reliance on fat metabolism at the expense of carbohydrate metabolism, more rapidly altering glucoregulatory function.

 

Edited by mccoy

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Study on the effects of light postprandial activity: 30 minutes light bicycling (but not so  light = 70% of max heart rate):

Høstmark, A. T., Ekeland, G. S., Beckstrøm, A. C., & Meen, H. D. (2006). Postprandial light physical activity blunts the blood glucose increase. Preventive Medicine, 42(5), 369–371.doi:10.1016/j.ypmed.2005.10.001 
 
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A consistent picture was obtained, irrespective of age and training condition (Fig. 1): in both trained and sedentary, young, and middle-aged women, the increase in blood glucose level after intake of cornflakes (1 g carbohydrate/kg body weight) was appreciably reduced when performing light bicycling physical activity for 30 min after finishing the meal. Post-exercise, the blood glucose concentration rose again, but the peak value was lower than that found without exercise. As found by repeated measures ANOVA, there was a significant main effect of time and interaction between time and exercise. P < 0.05 for the difference between corresponding mean values in the same panel at 30 and 45 min after the meal (paired t test with Bonferroni correction). We also calculated the difference in area under the curves (control experiment minus that involving post-meal exercise) for the time interval 15 to 75 min (where the curves differ). Using ANOVA, it was found that for the sedentary group the glycemic effect was greater in middle-aged than in young women (P = 0.04). Additionally, in middle-aged sedentary women, there was at 60 min a significant (P = 0.001) difference (1.5 ± 0.3 mmol/l) in blood glucose. These observations suggest that this group of women had the greatest benefit of post-meal exercise (Table 1). Glycosylation and oxidation caused by elevated blood glucose may be harmful. For example, glyco-oxidation of LDL seems to make this lipoprotein more atherogenic (Knott et al., 2003). Our results demonstrate an acute blood sugar reducing effect of light exercise and of a magnitude similar to that obtained by hypoglycemic drugs (Chiasson et al., 1996; Feinglos et al., 1997), even after intake of a large dose of high glycemic food. We suggest that the lowered glycemic response by light post-meal exercise could be due to increased glucose extraction in the working muscle. For the general public, a brisk walk (or any other form of light endurance exercise) could serve to blunt the blood sugar rise after carbohydrate ingestion. For patients, who are not fit for such activities, an even lighter exercise might have a similar effect. Studies are currently in progress to define the lowest work intensity required to obtain a blood glucose reducing effect.

 

 
 
Edited by mccoy

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By the way, extracted from the top article, I added the emphasys for nondiabetic people:

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higher postprandial glucose (PPG) concentration is a risk factor for cardiovascular disease (CVD) (27), mortality (34), and cognitive performance impairment (30) in patients with Type 2 diabetes. In addition, in nondiabetic populations, elevated PPG is a risk factor for coronary heart disease, ischemic stroke (24), and CVD (21). Endothelial dysfunction, which is predictive of a future cardiovascular event, is caused by hyperglycemia through oxidative stress (4). Furthermore, oscillating glucose levels increase oxidative stress more than constant high glucose levels and have a more deleterious effect on endothelial dysfunction (3). For these reasons, controlling PPG levels may prevent cardiovascular disease events.

 

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This is very interesting, since deals with postprandial walking, a classic of the glucose-lowering schemes

Nygaard, H., Tomten, S. E., & Høstmark, A. T. (2009). Slow postmeal walking reduces postprandial glycemia in middle-aged women. Applied Physiology, Nutrition, and Metabolism, 34(6), 1087–1092. doi:10.1139/h09-110 

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....the relationship between postmeal walking time and the blunting effect of such walking on postprandial glycemia indicates a dose-response influence of postmeal walking. This contention is supported by the observed linear relationship between the 2-h IAUC mean values and walking time. Furthermore, the blunting influence caused by walking seems to be increased when carried out for more than 15 min, as indicated by the difference in the slope of the blood glucose curve between the first 15 and the last 25 min of 40-min walking. Thus, it seems that the duration of postmeal walking is a crucial factor for attenuating the increase in the postprandial blood glucose concentration. Previously, the blunting effect on postprandial glycemia of 30-min bicycling at 70% of maximal heart rate (Høstmark et al. 2006) and 45-min bicycling at 57% of maximal oxygen consumption (Nelson et al. 1982) have been demonstrated. Despite the very low intensity of the present work, the blood glucose reducing effect obtained by 40 min of slow walking seemed to be approximately of the same magnitude as that observed in the previous studies. This would suggest that the duration of postmeal physical activity may be at least as important as the intensity in lowering postprandial glycemia. This suggestion is in accordance with a recent study by Aadland and Høstmark (2008) on healthy subjects, and is consistent with the recommendations of Galbo, Tobin, and van Loon (Galbo et al. 2007) in those with type 2 diabetes, that overall energy expenditure, rather than peak exercise intensity, is the primary determinant for reduction in postprandial blood glucose and insulin with physical activity. Despite higher glucose utilization in high-intensity exercise, the acute effect on postprandial glycemia obtained by moderate or very low-intensity physical activity may be as beneficial as the effect of vigorous activity.

 

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Thanks McCoy. Very interesting.

A few years ago I conducting extensive glucose measurements before and after meals and exercise. I found exactly what this post meal walking study found - namely that exercise after a meal effectively blunts glucose excursions, but you have to keep the exercise up for a while after eating; otherwise the glucose spike is simply shifted later in time rather than eliminated.

Ever since then I've been in the habit of exercising continuously for at least an hour, and almost always more than two hours after my single daily meal. This includes jogging 1.25 miles, light resistance training for 30min, walking my dog 1.5 miles, and then walking two miles at 15% incline on my treadmill while (as of late, resuming) wearing my cold vest.

--Dean

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Dean, the first thing which pops in my mind, besides the difficulties in checking these dang glucose peaks, is how you could engage in all that exercise just after your presumably large single meal!

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