How do Glycemic Index (GI) and Load (GL) affect your appetite?
When it comes to appetite, the glucostatic theory, the idea that we eat when our energy levels get low, is the trend at the moment. With continuous glucose monitoring (CSM) very popular for those with and without diabetes, how do different food sources affect your appetite and what is meant by Glycaemic Index (GI) and Load (GL)?
When it comes to energy, we break down foods to glucose to make energy in a process called respiration. This glucose is combined with oxygen to make ATP energy which fuels every cell in our body. Energy is measured in calories (Kcal) and some foods, such as fats which are 9 kcal energy per 100g, provide more energy than others, such as carbohydrates and proteins at 4kcal/100g. The glucostatic theory was first derived by a scientist called Jean Mayer in 1953. This proposed that blood glucose dips increase hunger and blood glucose peaks decrease hunger. Certain foods have since been found to raise blood glucose more than others. The ability of a food source to raise blood glucose is determined by its ability to be readily broken down to glucose by enzymes in food digestion. The theory is that the higher the GI, the more rapid the glucose spike and the more Insulin (the body hormone produced by the pancreas to lower blood glucose) is produced. This means a quicker and steeper glucose dip, providing quick but short-lived energy which increases appetite.
Simple sugars such as mono and disaccharides (or table sugar glucose, milk sugars lactose and galactose, fruit sugar fructose) are easily digested and broken down and so cause blood sugar spikes. These carbohydrates thus have a high glycaemic index (GI), as they rapidly raise blood glucose levels. Glycaemic load is simply the GI with the portion size taken into account. More complex sugars such as carbohydrates starches (medium GI) and fibrous non-starch-polysaccharides (NSPs), oligosaccharides and resistant starches, are more branched in structure or are insoluble (cannot be digested) and so have a smaller GI and GL. Proteins and Fats also have more complex structures and take longer to break down, and so have a smaller GI and GL.
What impacts Glycaemic Index?
It has been found that..
- A person's age/fitness level/stress/individual health status and the amount of sleep they have had.
- The chemical properties of the food- carb type/fat/protein etc
- The order in which components of a meal are eaten (eating fibre first reduces the glycemic index of a meal)
- The way it is cooked (raw foods are harder to digest than those boiled or sauteed)
- The portion size, the particle size of the carbohydrates (with ground almonds, for example, having a higher glucose peak that chewing a whole almond)
- The fibre content
- The fat and protein content of a meal
- The water content
- The level of activity you do before and after a meal (cardio exercise before reduces GI, as does a short walk after a meal)
- The speed at which the meal is eaten
- If the meal is consumed with an acid such as vinegar or citrus fruit
all affect the glycaemic index of a meal.
What foods are best to eat?
As you can see above, when it comes to glycemic index and glycemic load, it is not as simple as just eating low-GI foods. You have to prepare them properly and combine them with other foods in a meal that will reduce the GI peak. This being said, there are some foods that do cause very high glucose peaks. These tend to be more processed foods and simple sugars such as those in sweets and sweet deserts, potatoes and crisps, white rice and milled wheat (so white flour in breads and biscuits). Wholemeal flour is also mid-range GI as it is just white flour dyed brown with a little barley flour or bran added back. The best flour is wholegrain as it contains the whole wheat kernel with the bran (fibrous) layer and aleurone layer which is hardest to digest and therefore has the lowest GI. Adding fat and protein to your food also decreases GI and so wholegrain products with nuts and seeds or oils added have lower GI than those without. As a rule of thumb, the less processed a meal is, the better.
Overall?
Overall appetite is not as simple as just being down to the GI content of your food. This very reductionist viewpoint demonises simple sugars, encourages restrictive eating and promotes eating disorders. Appetite is hugely complex, linked to learned habits, your hunger gut signals, your hormones, your emotions, eating setting, level of sleep, if you are ill, your age, who you are eating with and so many other complex factors. There is no one rule for reducing appetite. The low-GI diet will not work for everyone and can make some people very unhealthy. The best thing to do is to do is to tailor your diet to you and your individual health status and work from there.
Copyright Laura Campbell 26/10/2022
