Are the Glycemic Index and Glycemic Load the Best Way to Know How Food Will Affect YOUR Blood Sugar?

Maintaining blood sugar (aka blood glucose) levels in an optimal range is critical to staying healthy. Blood sugar that goes up and down dramatically (aka the blood sugar rollercoaster) is associated with not only diabetes and hypoglycemia, but also heart disease, Alzheimer’s disease, and cancer. If you want to keep your blood sugar in the optimal range to preserve your health, it is helpful to understand how the foods you eat might affect it.

Of course, sugar, in all its forms, will increase blood sugar, but other carbohydrates also convert to sugar (glucose) after being eaten. Different carbohydrate-containing foods break down at different rates and can have different effects on your blood sugar. For example, foods with a high starch content, especially those that have been refined, such as flour, tend to strongly spike the blood sugar, while foods with little to no carbohydrates (such as non-starchy vegetables, olive oil, meats, eggs, and avocados) have hardly any effect on blood sugar levels. Planning meals and snacks around blood sugar-balancing foods is an important step to optimize your health, but how can you know which foods are best for you?  

The glycemic index (GI) was introduced in the early 1980s as a way to determine which foods raise blood sugar the most. It ranks carbohydrate-containing foods from 0 to 100, based on how high a food raises blood sugar levels in a two-hour period compared to a standard, usually sugar or white bread, which is assigned a GI value of 100.1 The portions of the test food and the standard provide 50 grams of carbohydrates (not counting fiber). The GI is supposed to tell us whether a food will raise blood sugar levels dramatically, moderately, or just a little.2 Theoretically, the higher a food ranks on the index, the greater its effect on blood sugar levels. But the GI value of a food alone does not tell you how a serving of that food will affect your blood sugar; you also need to know how much carbohydrate is in a particular food. For that you need to know the glycemic load (GL), which was created to make the glycemic index more useful. The GL takes into consideration a food’s glycemic index as well as the amount of carbohydrates per serving. Many foods have relatively high GI values but small amounts of carbohydrates, and it would take a large quantity to reach 50 grams of carbohydrate. For example, you would have to consume four and half cups of diced watermelon before you ingested 50 grams of carbohydrates. So, while the GI value of watermelon is high (72), the reality is that the blood sugar impact of eating a serving of watermelon (1 cup diced) for most people is minimal.

Although GI and GL values are somewhat useful, they are used on a limited basis (usually only in research) and their value in everyday menu planning is questionable. First, different people can have wildly different responses to the same food. Another major drawback to the GI and GL is that they do not offer insight into how fructose affects the body. Unlike glucose, which moves directly into the bloodstream causing a spike in blood sugar, fructose is instead metabolized in the liver, which means it doesn’t spike blood sugar. It does, however, cause “de novo lipogenesis”, or new fat formation, which usually manifests in the form of increased triglycerides. Therefore, a food that is low in glucose but high in fructose is not necessarily a healthier choice. Also, we rarely eat foods by themselves but instead in a meal of mixed foods, which also influences our blood sugar.

The only way to truly learn how specific foods affect your blood sugar levels and which carbohydrates you can safely eat without spiking your blood sugar is to invest in a glucometer (aka blood glucose monitor). This can be the finger prick type that you use upon waking and after meals or a continuous blood glucose monitor that attaches to the skin and monitors blood glucose day and night. You can monitor your blood sugar first thing in the morning and again 1 to 2 hours after eating for several days while eating a variety of foods (and especially those you eat the most) to begin to understand how the foods you eat affect your blood sugar. You don’t have to use the monitor forever, although you can. The optimal fasting blood glucose range (the measurement taken first thing in the morning) is between 82 and 88 mg/dL,3 4 5 6 7 while one hour post-prandial blood glucose (a measurement taken one hour after a meal) should be less than 140 mg/dL and the two hour post-prandial blood glucose (a measurement taken 2 hours after a meal) should be less than 120 mg/dL.8 Note, if you have been on a very low-carbohydrate diet for a while, your fasting blood glucose may be slightly elevated.9 This is usually not cause for concern if your post-prandial measurements are in the optimal ranges.

Another, albeit less accurate, method is to pay close attention to your energy, mood, and brain function before and after meals. Most of us will experience noticeable changes in these areas as our blood sugar goes up and down throughout the day. In general, feeling calm and focused, with steady energy and no cravings is a good sign your last meal was a balanced meal for you. However, if you feel tired or have too much energy, if you’re spacey and unable to concentrate, or you notice your mood dip or you’re having food cravings, that is a good sign your last meal was not a balanced meal for you.  

The best way to keep blood sugar levels under control is to follow the following steps.

Be aware that you may find through your blood glucose monitoring that your personal blood sugar-balancing needs may differ.

  • Maintain a well-balanced diet that focuses on proteins, fats, and complex carbohydrates (particularly emphasizing brightly colored non-starchy vegetables)
    • Examples of non-starchy vegetables include sweet peppers, spinach, chard, tomatoes, cucumbers, radishes, lettuce, cauliflower, cabbage, sprouts, artichokes, celery, zucchini, asparagus, broccoli, green beans, garlic, and Brussels sprouts.
  • Minimize (or avoid) processed foods such as sugar, flour, damaged fats, and foods containing them.
  • For those who are active and need more carbohydrates, emphasize nutrient-dense starchy vegetables such as winter squash, beets, and sweet potatoes. If grains are a part of your diet, choose whole grains like quinoa, buckwheat, and brown rice.
  • Eat fruits and starchy vegetables (e.g., rutabaga, winter squash, parsnips, celery root, white and red potatoes, sweet potatoes, yams, beets) along with protein, fat, and/or fiber. In fact, since protein, fat, and fiber slow down carbohydrate absorption, they should be included in every meal.
  • Exercise regularly.


  1. Venn, B.J., Green, T.J. (2007). Glycemic index and glycemic load: measurement issues and their effect on diet-disease relationships. Eur J Clin Nutr, 61(suppl 1), S122-S131. doi:
  2. Brand-Miller, Jennie, Ph.D. Wolever, Tomas, M.D., Ph.D., Colagiru, Stephen, M.D., & Foster-Powell, Kaye. 1999. The Glucose Revolution. Marlow & Company, New York.
  3. Shin, J. Y., Lee, H. R., & Lee, D. C. (2011). Increased arterial stiffness in healthy subjects with high-normal glucose levels and in subjects with pre-diabetes. Cardiovascular diabetology10, 30.
  4. Bjørnholt, J. V., Erikssen, G., Aaser, E., Sandvik, L., Nitter-Hauge, S., Jervell, J., Erikssen, J., & Thaulow, E. (1999). Fasting blood glucose: an underestimated risk factor for cardiovascular death. Results from a 22-year follow-up of healthy nondiabetic men. Diabetes care22(1), 45–49.
  5. Nichols, G. A., Hillier, T. A., & Brown, J. B. (2008). Normal fasting plasma glucose and risk of type 2 diabetes diagnosis. The American journal of medicine121(6), 519–524.
  6. Zhou, L., Mai, J. Z., Li, Y., Wu, Y., Guo, M., Gao, X. M., Wu, Y. F., Zhao, L. C., & Liu, X. Q. (2018). Fasting glucose and its association with 20-year all-cause and cause-specific mortality in Chinese general population. Chronic diseases and translational medicine5(2), 89–96.
  7. Wei, M., Gibbons, L.W., Mitchell, T.L., Kampert, J.B., Stern, M.P., Blair, S.N. (2000). Low fasting plasma glucose level as a predictor of cardiovascular disease and all-cause mortality. Circulation, 101(17).
  8. Kresser, C. (2019, March 17). How to prevent diabetes and heart disease for $16. Retrieved December 13, 2021 from
  9. Berger, A. (2018, July 12). Higher fasting glucose on ketogenic diets: reason to worry? Retrieved December 13, 2021 from