I’ve seen lots of people saying that the cause of T2DM is genetic. usually as a way to deny responsibility in the condition: if it’s genetics, there is nothing they can do about it, and therefore there is nothing they need to do. They have diabetes, and that’s it, they’re just unlucky.
But that’s not an honest stance and isn’t accurate. It is true that there is a part of genetics in the condition: 72% of people with a BMI > 40kg/m2 don’t have diabetes. If genetics weren’t involved, there should be a threshold above which everybody would be diabetic.
- The accumulation of fat in the liver damages its insulin sensitivity, leading to an increase in glucose secretion into the bloodstream. This is particularly noticeable in the fasting state (hence the important check of fasting glucose). This has been known since the early 2000s.
- The exposure of pancreas’ Beta cells to triglyceride and fatty acids decreases their ability to respond to acute increase in glucose levels. This has been known since the mid 90s. In turn, it disables the role of the liver in glucose regulation (as the liver responds to insulin secretion from the pancreas).
The source of the diabetes is therefore excess fat storage, not genetics. The genetic predisposition most likely creates favourable conditions in which an excess of calorie intake (and fat storage at inappropriate locations such as the liver and the pancreas) has an increased effect on liver and pancreas functions that leads to elevated levels of blood glucose, and therefore diabetes.
And as fat is the source of these 2 conditions that combine to generate diabetes, rapid weight loss is the obvious course of action to fight diabetes as soon as possible after diagnosis, as shown by several studies (e.g. Counterpoint, Counterbalance, DiRECT, Look AHEAD). That course of action isn’t impeded by genetics.
The same way you might be predisposed to certain forms of cancer or certain illnesses, genetics play a role in T2DM. But they are not the cause. The cause is lifestyle choices exacerbating these genetics traits. Lifestyle choices can be changed.