Glycemic Load

I’m teased a lot in my family for a saying of mine – that I believe all human beings are “pre-diabetic” – that is, all human beings face some risk of acquiring Type 2 diabetes. And it's on the rise.

Findings related to the glycemic load in our diets prove once again, it’s not just important how many calories you consume – the kind of calories you consume is important, too.

Glycemic index (GI) tells you, from the point of view of your bloodstream, how sugary a food is – that is, how quickly the glucose from that food makes its way into your bloodstream. A food with a high GI has very “accessible” glucose; a food with a low GI is like a long-acting drug, and glucose gets released from it more slowly. Starchy foods like potatoes and white bread have very high GIs.

Glycemic load (GL) is, in my view, a much more useful bit of information: it tells you how much glucose will actually get into your bloodstream from a portion of a particular food.

For instance, people look at tables of foods’ GIs and get very sad to see that watermelon, which we all love, has a relatively high GI. But watermelon is mostly water, so while its GI is something like 72, a 100g slice is 95g water and only 5g carbohydrate, so it only has a GL of 3.6.

So, from the point of view of your bloodstream, a small amount of a high GI food has the same effect, or the same glycemic load, as a large amount of a low GI food.

Why care about GL? Because, blood sugar spikes are bad for us in a number of ways, whereas keeping blood sugar relatively constant is better for our bodies.

Blood sugar spikes require insulin secretion (to “mop up” the excess blood sugar), and more often, insulin converts the excess sugar into fat, making us fat.

Often, our bodies secrete too much insulin to “mop up” excess blood sugar when it spikes, and then that precipitates dangerous blood sugar lows, which make us feel hungry and low-energy, which leads us to eat more sugary stuff and repeat the vicious cycle.

Excess fat and volatile blood sugar levels increase our risk of acquiring Type 2 diabetes, and blood sugar spikes cause inflammation and oxidative stress (extended high blood insulin is damaging to body tissues and moreover seems to elicit inflammatory prostaglandin response), which can lead to chronic disease.

Caveat: Being able to assign a range of values to describe different carbohydrates more precisely is definitely more informative than the binary categories "simple" and "complex." But (sorry for the bad pun here) we should take these measurements with a grain of salt:

• The same exact food can test at widely varying GIs – baked Russet potatoes apparently have tested as low as 56 and as high as 111, and the same exact piece of fruit has a lower GI when unripe and a higher GI after it ripens (fruits convert more complex starches into sugar as they ripen, which is why they taste sweeter ripe);
• Food processing, like pickling and cooking, increases foods’ GI values (your body can “access” the glucose in something cooked easier than in something raw that’s more difficult to break down and digest); and
• There are also individual differences to take into account, and the same person's ability to digest starches can be different at different times of the same day.

Generally, there is reason to believe that a low GL diet is better for us humans. In addition to being proven to help overweight people lose excess weight, a low-glycemic-load diet provides other benefits: lower inflammation, lower blood pressure, lower heart disease risk, less insulin resistance, and lower lipid levels. Even in people with healthy weights, researchers think that reducing glycemic load might help to prevent or treat obesity, cardiovascular disease, and diabetes mellitus. Individuals on low GI diets after many years have a lower risk for developing both Type 2 diabetes and coronary heart disease.

More Resources:

1. Harvard: Glycemic index and glycemic load for 100+ foods
2. Wikipedia: List of foods and their glycemic load
3. The University of Sydney: Glycemic Index Database
4. NutritionData.com: "Glycemic Index"
5. Effects of a Low–Glycemic Load Diet on Resting Energy Expenditure and Heart Disease Risk Factors During Weight Loss. Mark A. Pereira, PhD; Janis Swain, MS, RD; Allison B. Goldfine, MD; Nader Rifai, PhD; David S. Ludwig, MD, PhD. JAMA 292: 2482-2490, 2004.
6. Carbohydrate intake, glycemic index, glycemic load, and risk of postmenopausal breast cancer in a prospective study of French women. Lajous M, Boutron-Ruault MC, Fabre A, Clavel-Chapelon F, Romieu I. Am J Clin Nutr. 2008 May; 87(5): 1384-91.