The GI myth in weight loss: what actually matters
The glycemic index sounds like a simple answer: choose low-glycemic foods and the fat starts to disappear. Real life is unfortunately messier. If you want to lose weight or support your training, the whole meal, the calories and the quality of the food count for more.
GI and why it sounds so convincing
It is unusual to devote an entire article to taking down a single diet idea. But the glycemic index, or GI, has for years circulated in newspapers, nutrition books and gym talk as such a confident promise that it is worth pausing to ask calmly: what actually happens?
GI stands for glycemic index. It is measured by taking at least ten people and looking at the area under their blood sugar curve for two hours after they eat a specific food. That result is compared with what happens when the same people get the same amount of carbohydrate as glucose. The average ratio is multiplied by a hundred, and that gives you the glycemic index value.
An important difference: the glycemic index is not the same as the II, or insulin index. The glycemic index looks at blood sugar. The II looks at the insulin response. In an everyday meal the two can behave quite differently.
How does the GI idea work in weight loss?
The theory is simple. When blood sugar rises quickly, more insulin is released. Insulin helps store energy as glycogen in the muscles and liver, and some of the energy can end up in fat cells. This leads to a tempting conclusion: the lower the glycemic index, the less insulin and the less fat.
Honestly, it sounds logical. That is exactly why glycemic index thinking has sold so well. The problem is that the body does not work like an Excel spreadsheet, and a meal does not usually consist of one bare food.
The first problem is the measurement itself. The glycemic index values for kidney beans have ranged between 13 and 70 across different sources. For a baked potato, figures between 56 and 111 have been reported. For a banana, between 30 and 70. When one and the same food can vary so much between tables, it is very hard to turn it into a firm everyday rule.
The second problem comes from portion sizes. The glycemic index is measured based on 50 grams of carbohydrate. That puts low-calorie foods in a strange light. The classic example is cooked carrot, whose GI can be over 80. But to get the amount of carbohydrate needed for the measurement from carrots, you would have to eat about 630 grams of them. Most people do not do that alongside their lunch.
GI does not describe a whole meal
Few people sit down at the table and eat nothing but a bowl of boiled potatoes. Usually there is meat, fish, eggs, sauce, salad or a glass of milk next to it. Fat and protein change how a meal is absorbed. So the GI of a single carbohydrate source no longer says very much about what happens after the whole meal.
The same goes for insulin. GI measures the blood sugar response, but it does not reliably show how much insulin the body releases after a meal. Milk, for example, has a low GI but a high II. The reason is the protein in milk. Whey can trigger as strong an insulin response as the same amount of glucose.
That does not mean milk is bad or whey is bad. It simply means GI is not a sufficient tool when you are trying to assess the nutrition of someone who trains, or their weight loss.
What should you actually keep an eye on in weight loss?
A simple truth: GI is not a magic button for weight loss. When calorie intake drops, weight falls. When you consistently take in more calories than you burn, weight rises. The old principle, energy in minus energy out, still holds.
The original claim that low-GI food will surely keep you full for longer is not that certain either. According to one 2005 study, there was no clear difference in appetite between eating high-GI and low-GI food. Appetite is also affected by portion size, protein content, dietary fiber, fat, sleep and stress.
This also explains why a friend may have lost seven kilos on a “GI diet”. Often the result did not come from the GI table, but from the person cutting calories at the same time. When you cut carbohydrates, the amount you eat often drops automatically. It is much harder to overeat tuna than sandwiches.
Another reason is that some low-GI foods simply are good choices. They can contain plenty of dietary fiber, give a better feeling of fullness and fit well alongside training. But then the benefit comes not from a magic GI number, but from the overall quality of the food.
GI and the practical choice for people who train
For someone who trains, GI is a rather poor main yardstick. On a pre-contest diet or in ordinary weight loss, it will not rescue a bad plan. If your insulin tolerance is fine and your training is regular, all the talk about steadier blood sugar is usually not the most important thing.
So what should you do? Eat enough high-quality protein, add healthy fats and choose carbohydrates that give you energy and suit your digestion. Watch your portions. Move more if your goal is to lose weight. And don’t turn nutrition into a table hunt where every banana needs its own court hearing.
GI does have one good side effect, though. It got many people thinking about what they put in their mouths. It used to be that most people believed that if the label said “light”, the kilos would melt away. Today even a seven-year-old knows that sugar traps can hide in very ordinary products. That growth in awareness is not a bad thing.
But if your goal is a better physique, don’t get hung up on GI. Keep your focus on your whole menu, your training and your consistency. Leave GI to the newspapers to worry about.
Translated from Body magazine. Author: Andreas Guiance
FAQ: GI and weight loss
Does low-GI food always help you lose weight?
No. You lose weight when you burn more energy than you get from food. Low-GI food can help you make better choices, but eating by GI alone does not guarantee weight loss.
Does high GI mean a food is bad?
Not always. A food’s effect depends on the amount and on the whole meal. If you eat carbohydrate together with protein, fat and dietary fiber, your body’s response can be quite different from what the single number in a table suggests.
Should someone who trains use a GI table?
You can take a look, but it shouldn’t be your main tool. For someone who trains, what matters more is daily energy intake, protein intake, how well you tolerate foods, and whether your menu supports your workouts and recovery.
Author: Greta
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