The parts that make up our bodies conspire at all times to keep us alive. Our cells require constant energy to function. Some of these cells can function off of a variety of fuels, such as how our muscles can utilize ketone bodies, fatty acids or glucose for fuel. Other cells, such as those that make up the brain are more discerning. The brain requires glucose as its sole source of energy, which means that in order to keep our nervous system functioning the body must make sure there is adequate glucose available.(1) Various mechanisms in the body work together to tightly control blood glucose levels to make sure that your organs have enough fuel to continue operating optimally. There’s two sides to this coin though as both too little glucose (hypoglycemia) and too much glucose (hyperglycemia) are very harmful to our health and even potentially fatal.
When you consume foods containing carbohydrates, your body breaks these down into glucose which is then absorbed in the small intestine and shuttled into the blood stream. This is when your blood glucose levels begin to rise, sending a signal to your pancreas to release the hormone insulin. Insulin takes the glucose from your blood and ushers it directly into cells. When insulin has done its job properly, the blood glucose levels will return to a balanced baseline.
Different foods affect blood glucose levels differently. As I mentioned earlier, your body needs to keep glucose tightly controlled. If there is a huge rush of glucose that surges into the blood stream following a meal of carbohydrates, the pancreas will need to respond in kind with large amounts of insulin.
The Glycemic Index and Glycemic Load were developed as a way to measure the amount of blood glucose that will be delivered following the ingestion of a particular food. Although somewhat oversimplified, these measures can be valuable tools to express the different qualities of a food.
The Glycemic Index assigns a numerical value to a food based on how blood glucose levels respond, where pure glucose is the highest reference number at 100. Higher values signify that the food will cause a larger increase in blood glucose levels, leading to an abrupt demand for insulin to regulate.
The Glycemic Load utilizes information from the Glycemic Index but takes it a step further by assessing how much a serving of food will increase blood glucose levels. The formula that is used to calculate Glycemic Load is (Glycemic Index x Grams of Carbohydrates per Serving)/100. A Glycemic Load is considered low when its 10 or below, and is said to be high if it’s 20 or above.
The Glycemic Index and Glycemic Load may be oversimplifying things a bit, so let’s go over what some of their limitations are. First of all, the relationship between Glycemic Index and Glycemic Load is not straightforward and can be a bit confusing. For example, if you eat a small amount of a high Glycemic Index food it may actually have a low Glycemic Load. The same could be true vice versa where a low Glycemic Index food eaten in large amounts may have a high Glycemic Load. Remember that Glycemic Load is calculated based on the grams of carbohydrates per serving portion consumed. If we look at watermelon for example, it is a high Glycemic Index food, but the Glycemic Load for a serving (100g) is low because it only contains 5g of carbohydrates.(2) This variability can make it hard to quickly understand how a specific food may affect your blood glucose levels.
The second limitation is that the Glycemic Index and Glycemic Load do not measure the quality or healthfulness of a food. If a food has a low number of carbohydrates per serving it will keep the Glycemic Load low – this could be true even if those carbohydrates are 100% sugar (sucrose). So, where someone may think that they are making a healthy food choice by choosing something with a low Glycemic Load, the food may not be very nourishing. I see this often in foods marketed to diabetics where the foods are rated with a low Glycemic Load but actually contain highly processed and inflammatory ingredients.
Third, the Glycemic Index and Glycemic Load don’t take into account ‘mixed meals’ where carbohydrates are consumed with proteins or fats. These macronutrients, along with resistant starch and fiber content can have a big influence on a food’s actual blood glucose effect by changing the rate and availability of glucose absorption.
Lastly, Glycemic Index and Glycemic Load don’t account for individual variability of blood glucose response. Bio-individuality means that each of us will interact with our food environment differently and Glycemic Index and Glycemic Load can’t measure how much one person’s blood sugar will rise versus another’s. Many people may find that they have poor insulin response, either from pancreatic insufficiency or insulin resistance and they aren’t able to control their blood glucose well.
Although it can be helpful to talk about foods using Glycemic Index and Glycemic Load, it’s really the quality and balance of diet that will have the largest impact on our health. When we eat processed foods such as flour (yes, even gluten-free) or sugar (yes, even coconut sugar), they are essentially pre-digested, allowing for them to be fully broken-down and absorbed in the small intestine. Minimally processed carbohydrates consumed with proteins and fats can help to slow the absorption of glucose into the blood stream, requiring a less dramatic response from insulin. Choosing to fill our plates with unprocessed sources of carbohydrates like starchy vegetables, raw fruits, and whole kernel grains will yield many benefits and support our body’s effort to thrive.