We all know someone who can eat carbohydrates all day, everyday and not gain a kilo. However, I’m sure we also know those people who so much as look at carbohydrates and they put on weight. But why is that? Well, it may be due to different peoples carb tolerance based on their genetic profile.
Carb tolerance. What is it?
All humans have a gene called AMY1. This gene codes for the enzyme amylase, which is responsible for carbohydrate digestion in the mouth. Research is starting to show that there are variations in the number of copies of AMY1 genes between people. The genes can range from two to sixteen copies. The more AMY1 genes you have, it means the more salivary amylase. More salivary amylase means you break down carbs more effectively, immediately.
As soon as you bite into a carbohydrate rich food, your AMY1 genes go to work based on taste receptors that detect carb in take. And again, if you have more AMY1 genes, your carb-digestion will be more efficient.
Observational research has demonstrated that individuals who have more copies of this gene, produce more amylase enzymes and have lower BMI’s. If you have more than nine copies of AMY1 then you are eight times less likely to be obese compared to someone who has fewer than four copies of AMY1. In other words, more amylase equals less body weight. And vice versa.
There are a few mechanisms as to why more amylase production is correlated with lower body weight. Firstly, the more amylase means more digestion of carbohydrates in the mouth. This means foods may taste sweeter and feel richer. As a result, people with more amylase might feel satisfied eating less. This also helps explain why eating slowly generally promotes weight loss (or maintenance). The more slowly we eat, the more we digest in the mouth. This in turn might lead to feeling “satisfied” with less food.
Secondly, people with more AMY1 copies tend to have a better insulin response after the ingestion of carbohydrates, meaning that the glucose is taken up into cells more efficiently and use the glucose for energy production, rather than lingering in the blood causing high blood glucose levels, which eventually form fats.
Thirdly, different amylase concentrations essentially result in different rates of carbohydrate absorption of the same food, or a different glycemic index for each person eating a given food. Therefore, to a carb tolerant person, a banana may be low GI, where is to a carb intolerant person, it may be high GI.
All of these findings can potentially explain why cultures like the Japanese have high carbohydrate diets and are relatively lean. Population studies have shown that Japanese people have more copies of AMY1 (average 7). Variations in these genes probably played an evolutionary purpose at some point in human development, where cultures that had higher carbohydrate diets like the Japanese and pacific islanders (from fruit) needed more of these genes to handle their high carbohydrate diet.
This makes a lot of sense if you think about it. After all, if you eat more starch, you need more of the enzyme that breaks down starch. However, in our modern world, with the high carbohydrate foods readily accessible to everyone, people who have less copies of these genes are more likely to put on weight, become insulin resistant (i.e. diabetes), have increased triglycerides, increased blood lipids and increased blood glucose levels. Also, they are more likely to develop diseases like diabetes and heart disease. It is also important to note that there are variations in carb tolerance between people is on a spectrum, rather than just being tolerant or intolerant.
Lastly, I’m not saying that this one genetic variation is the only factor at play to weight gain and disease development, however it is definitely an interesting contributing factor.
What to do?
If you think you may be carb intolerant and may have a lower amount of AMY1 genes as you struggle with your weight and blood glucose levels, try these strategies:
1. Eat slowly and chew your food thoroughly. It may sound simple. (And this strategy is far too often overlooked). But by eating slowly, you give whatever amylase you do have more time to break down the carbohydrates you just ate. This puts you in the same position as someone with more amylase who eats faster.
2. Use probiotics. Studies suggest that lower amylase (and associated obesity) might be related to negative changes in the gut flora. This is interesting because we know our gut bacteria play a role in gene expression. Therefore our gut bacteria can either turn on or turn off these AMY1 genes. Poor gut flora can cause a down regulation of these AMY1 genes, therefore decreasing a persons carb tolerance. So if you already have a low number of copies of this gene and you have poor gut flora, it can cause a decrease expression of AMY1. This demonstrates how our diet and lifestyle can influence the expression of our genes, because we know that our diet and lifestyle has a profound impact on the composition of our gut flora. It is said that genes load the gun but the environment pulls the trigger. It means that many of our genes are not set in stone. Just because we have a predisposition doesn’t mean this will be expressed, unless we engage in poor diet and lifestyle habits. Because of this mechanism, probiotics can’t hurt, as we do know that poor gut health is closely related to many diseases including obesity. Repairing the gut flora may also be a large part of a weight loss program. I have also written extensively about gut health here.
3. Keep eating healthy carbs. This means high-fiber, nutrient-rich foods like beans, legumes, potato, sweet potato, minimally processed whole grains, and colourful fruits and vegetables. People with lower amylase may benefit from eating slightly fewer carbs than people with high amylase, but going super low carb probably isn’t the answer.
4. There is a big difference between processed and refined carbs compared to whole-food carbs like potato and sweet potato. Whole-food carbs are more nutrient dense and lower in calories, therefore you feel full after less amount of calories, even if you are more carb intolerant. However, processed and refined carbs are high in calories but low in nutrient density, which means you will have to consume higher amounts to feel full as calorie density has little effect on satiety, where is nutrient density does. This is obviously a large problem for a carb intolerant person based on the mechanism explained in this article and it can lead to overshooting their caloric intake. Therefore, most people can tolerate a modest amount of whole-food carbs in their diet, some might have to be a little more careful.