September 28, 2021

I, Science

The science magazine of Imperial College

Jennifer Graudenz takes a look at reports of the vegan diet's role in treating type 2 diabetes.

In the last decade, some scientific studies showed that for people suffering from type 2 diabetes, a low-fat plant-based diet can improve glycemic control and reduce the need for medication. While we have since seen an often sensationalist reporting of these claims, many are still left wondering if the science is real, and just how much a dietary change really could affect diabetes.

sugar level testing on fingersType 2 diabetes occurs with insulin resistance, meaning that the cells in the body become  immune to the insulin produced by the pancreas. Insulin production may even cease completely. Consequently, glucose stays in the blood instead of being used as fuel resulting in high blood sugar levels and the development of clinical signs such as increased urination, thirst and fatigue. Long-term consequences of diabetes are severe, reducing life expectancy and can cause a range of complications, from kidney failure to dementia.

A cure is much needed, and despite best efforts, one is still not available. Could a plant-based diet be the answer?

… Is it weight loss?

While there are several studies indicating the benefits of a plant-based diet, there is no definite consensus on why or how these benefits work. A very popular opinion is that vegans consume less fat, including both saturated and total fat consumption. This leads to a reduced caloric intake and hence weight loss. Type 2 diabetes is positively associated with obesity; in fact, obese people have a seven times higher risk of developing the disease.

chart showing the amount of people with type 2 diabetes in different weight categories and of different ages

“Figure 3”: Percentage of people with type 2 diabetes categorised by their weight in 2009/2010. A clear association between diabetes and obesity can be seen. 

However, there are several points which need to be considered. Firstly, not all obese people develop diabetes and secondly, people with normal body weight can have type 2 diabetes as well. Would it be possible for an obese person to cure their diabetes through weight loss, whilst a slim person found it impossible to do so? There is no absolute correlation between losing weight and not eating meat. A vegan can still thrive on a diet of processed pizza and chips. You could therefore conclude that a plant-based diet may reverse diabetes only if:

  1. The diabetes is caused by obesity.
  2. The plant-based diet is healthy and results in weight loss.

This means a reversion is theoretically possible, but not guaranteed. Indeed, a 2009 study conducted by the American Medical Association on American Adventists compared vegetarian people to non-vegetarian people and suggested that even after adjustment for body weight, vegetarians still had a lower diabetes rate. In practice this means that weight had little to no impact on diabetes. While these results cannot easily be generalised, it implies that other factors influence disease reversal.

… Is it a reduction in lipid accumulation?

Another, slightly more complex theory is that a plant-based diet leads to reduced accumulation of intramyocellular lipid (the fat stored in muscle cells) accumulation. This improves insulin sensitivity and increases carbohydrate tolerance. It has been proposed that these fats are the main culprit of insulin resistance because the fatty acids released by them are thought to compete with the glucose in the blood. In short, less stored fat means less competition so insulin can reach the cells more easily.

It makes for a convincing theory. If there is insulin, however, type 2 diabetes occurs through a resistance to or lack of insulin. In the first instance, a reduction of fats stored in muscle cells may relieve the disease, but it would be utterly useless in the second instance. Knowing this, we could surmise that plant-based diets may only improve type 2 diabetes in select cases.

… Is it a low GI diet?

A third theory is that a diet of low GI carbohydrate foods may be responsible for the diabetes reversal. “GI” stands for “Glycaemic Index” and measures how much the blood sugar rises after consuming a meal. High GI foods raise blood glucose more than a food with a medium or low GI. Barley, pasta and sweet potatoes are some examples of low GI foods, whereas high GI food includes white bread and white rice. A number of studies have shown that a diet consisting of low GI foods have beneficial effects on insulin sensitivity, because there is less of blood sugar spike after consumption. A low GI diet should, however, be considered separately from a vegan diet, as meat is also a low GI food.

So, although the exact mechanisms and reasons for the beneficial effects are still unknown, and a variety of factors need to be taken into account, it seems logical that these three factors may play a role in the reversal of type 2 diabetes.

Whilst modern-day nutritional research maintains that no single component of our diet is a perfect solution, it may well be that, in the case of reversal of type 2 diabetes, a combination of dietary components could certainly help.
Pass us the curly kale please!

kale salad

Jennifer Graudenz is studying for an MRes in Clinical Research

Images: Diabetes blood test, Piotr Adamowicz. Figure 3, Public Health England. Kale salad, Foodio.