If you’ve read my book, you know that I talk a lot about your uniqueness, and how that affects your response to altitude, training, etc. Here’s another study which confirms this.
Researchers at Tufts University published a study that examined differences among people’s glycemic index (GI) for white bread. Recall that the GI measures the degree to which a food changes blood sugar levels. Low GI foods (most fruits, pasta) have little effect on your blood sugar, while high GI foods (potatoes, carrots) cause a spike in blood sugar.
While white bread has a published GI of 72, the fourteen test subjects had average GI values that ranged between 44 and 132! And, the measured GI of white bread varied a lot within some individuals (they measured GI three times in each person).
So your response to a food might be quite different than you would expect, based on the published values. Knowing how your body responds to food, dehydration, altitude, etc. will allow you to tune your approach for better performance.
Citation: Vega-Lopez, S., L. M. Ausman, et al. (2007). Interindividual variability and intra-individual reproducibility of glycemic index values for commercial white bread. Diabetes Care 30(6): 1412-7