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Does Glycemic Response to Food Really Affect Appetite?



GI-Foods-7-HealthA popular narrative by proponents of low-glycemic index foods is the notion that high-glycemic index foods lead to a surge in plasma glucose, which in turn stimulates a spike in insulin levels, resulting in a rapid drop in blood glucose levels and an increase in appetite (“crash and crave”).

While this narrative is both biologically plausible and has been popularised by countless low-GI diets and products, the actual science of whether this story really holds true is less robust that you may think.

Now, a study by Bernd Schultes and colleagues, published in Appetite, seriously challenges this narrative.

The study was specifically designed to test the hypothesis that inducing glycemic fluctuations by intravenous glucose infusion is associated with concurrent changes in hunger, appetite, and satiety.

Using a single blind, counter-balanced crossover study in 15 healthy young men, participants were either given an i.v. infusion of 500 ml of a solution containing 50 g glucose or 0.9% saline, respectively, over a 1-h period.

On each occasion, the infusions were performed one hour after a light breakfast (284 kcal).

I.v. glucose markedly increased glucose and insulin concentrations (peak glucose level: 9.7 vs. 5.3 mmol/l in the control group); peak insulin level: 370 vs. 109) followed by a sharp decline in glycaemia to a nadir of 3.0 in the glucose study vs. 3.9 mmol/l at the corresponding time in the control condition.

Despite this wide glycemic fluctuation in the glucose infusion condition, the subjective feelings of hunger, appetite satiety, and fullness did not differ from the control condition throughout the experiment.

Clearly, these findings speak against the conventional narrative that fluctuations in glycemia and insulinemia represent major signals in the short-term regulation of hunger and satiety.

Or, as the authors put it,

Our findings might also challenge the popular concept of low glycemic index diets to lose body weight. Advocates of this dietary approach often argue that large glycemic (and concurrent insulinemic) fluctuations induced by the intake of high glycemic index foods can trigger feelings of hunger and, thus, on the long run favor weight gain. Our results argue against this notion since the sharp drop in circulating glucose after the end of the glucose infusion remained without effect on hunger ratings, at least within the time period covered by our experiment.

As they further note, these findings may explain why,

“…several clinical dietary intervention trials have failed to show an advantage of low glycemic index dietary approaches for weight loss in overweight/obese subjects in comparison with other dietary approaches.”

The lesson here, I guess is that, just because there is a seemingly compelling narrative to support an idea, it does not mean that that’s how biology in real life actually works.

@DrSharma
Edmonton, AB

5 Comments

  1. A bolus of IV glucose is much different than the complex sequence of events that occurs when we smell, taste, chew, and digest foods through the normal route. The results are interesting, but I’m not sure it really tells us too much other than, “glucose elevations and depressions alone do not affect appetite.”

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    • That is indeed true except that the proponents of the high-GI related “crash and crave” hypothesis use the fluctuations in blood glucose and insulin levels as the explanation for a potential increase in appetite and weight gain – this study just shows that things are clearly not that simple.

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  2. I agree with Buddy that this study’s conclusions cannot be extrapolated to actual appetite responses to low vs. high GI foods. After eating, numerous gut hormones (GLP-1, GIP, ghrelin) are released which affect appetite, satiation, and satiety. An IV administration of glucose cannot measure the effect of foods on any of these hormones.
    If the authors really wanted to know whether a low vs. high GI diet had different effects on appetite, they probably should have just fed actual low vs. high GI foods and then asked them about the feeling of hunger, satiety, and fullness.
    The only conclusion you can really draw from this study is the giving IV glucose doesn’t affect appetite.

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  3. I found it interesting that the subject pool was solely comprised of ’15 healthy young men’.

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    • I find it interesting that the published GI values for foods are based on the responses of ’10 healthy University students’.

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