I’ve been counselling people with diabetes for nearly 20 years and I continue to encounter a lot of confusion and misinformation about how best to manage diabetes with diet. Concepts like the glycemic index (GI) are no exception. People are routinely told [and confused] to eat foods with a lower a GI but what does that practically mean and is healthy eating as easy as assigning a number to a food?
What is the glycemic index?
Simply put, the GI is a measure (or metric) of a food’s ability [specifically food that contains carbohydrate] to raise blood sugar: in theory, the higher the GI, the greater the impact. The GI of a food is ranked as high [>70], medium [56-69] or low [<55]. The GI was originally created for research purposes, where the goal was to try and determine how a food, eaten under special research conditions, would impact a person’s blood sugar level. It furthered our understanding of carbohydrate metabolism but in my opinion, it should never have become ‘mainstream’.
Is healthy eating as simple as a number?
As a strategy for healthy eating, diabetes and blood sugar management, many people with diabetes have been advised to avoid, or limit, foods with a high GI but can it really be that simple? The GI of parsnips (a nutritious vegetable) has a GI of 80 – 92 [high] but the GI of table sugar [no nutritional value] is 58 [medium]. Likewise most chocolate bars have a medium GI [56-69]. Using the GI alone, it’s easy to see how less healthy foods could be chosen over healthier options and I encounter this in my practice. Clients are almost afraid to eat carrots, parsnips or potatoes because they think they have too much sugar or will lead to weight gain but then are confused when they see charts listing ice cream as a presumably better option give than it has a lower GI. What’s going on?
Most resources on the GI give overly simplified examples such as choosing 100% whole grain rye crisps instead of highly refined rice crackers or soda crackers (Saltines), or 100% whole grain breads instead of white bread, but also go as far as advising people to stay away from Russet potatoes, popcorn, Bran flakes, and black bean soup. See here and here for examples.
The GI of food, or meal, is affected by many factors such as the total amount of carbohydrate (or portion sizes), type(s) of sugar, presence of fat, protein, and fibre to name a few. This is why a chocolate bar may have a medium GI; the presence of fat, protein, and fibre in the nuts will slow down the absorption of the carbohydrate from the added sugar whereas the parsnip is nearly all carbohydrate. The GI fails to take into account a few key considerations, making its use as a simple guide for blood sugar control limiting, such as the amount, or portion size, of food eaten, the quality of the food, whether or not other foods containing factors that affect the GI are included as outlined above.
I guess it’s not surprising then that the glycemic index is still being defended and attempts are still being made to convince people that it makes sense and then persuaded to use it some 20 years later.
What to do?
As an educator I do my best to deliver direct, easy to understand messages with an appropriate dose of context. I personally don’t like the GI because in practice I’ve never found it to work well because of the limitations already mentioned. People eat food and I find it easier to talk about strategies that are appropriate to an individual’s situation that help to keep blood sugar levels in a healthy range with tips like the following.
- ‘Lower & moderate carbohydrate’ diets are not four-lettered words nor bad ideas and are a valid approach to diabetes management. See here
- Limit or avoid fruit juice (whole fruit is better because it has fiber).
- Limit the amount of starch-rich carbohydrate foods like pasta, rice, bread, buns, bagels, corn, potato, sweet potato, and yes pulses [chickpeas, lentils, peas & beans]; 60 – 70% of the calories in pulses come from carbohydrate and although they are rich in protein, they tend to impact blood sugar like a starch.
- Choose more non/low-starch vegetables like broccoli, cauliflower, kale, celery, radish, cabbage, asparagus etc. or those that ‘grow above the ground’ for the most part.
- Include controlled amounts of fiber-rich foods [100% whole grains, non-starchy vegetables, nuts, seeds or small amounts of pulses] at each meal.
- Don’t be afraid of fat, it’s an important source of calories as you reduce carbohydrates. Choose butter, olive, avocado, macadamia nut, or coconut oil. Don’t overly obsess about choosing fat-free dairy or extra lean meats. Don’t fret about saturated fats either, we’ve learned they’re not as bad as we once thought. See my post on this topic here.
- Include a good portion size [size of a computer mouse] of protein and each meal.
- Avoid sources of trans fat.
- Increase your intake of omega-3 fats from fish & seafood. Or supplements if needed [fish, calamari or algae]
- Limit foods with added sugars [don’t be fooled by ‘natural’ sugars], and refined/processed fats, especially omega-6 rich grain/seed/vegetable oils [canola, sunflower, safflower, soy, corn, grapeseed] or margarine, mayonnaise, commercial salad dressings made with them.