Type 2 diabetes is a condition where someone has too much glucose in their blood, and hence the body produces too much insulin that doesn’t work well. Many different factors, including our diet, can impact the amount of glucose in our blood.
The best diet for people with type 2 diabetes
Over the last 25 years, we have seen a rise in the number of people living with type 2 diabetes, not only in the UK but around the world. In the UK, the number of people diagnosed with diabetes has more than doubled in the last 20 years. In 1996, there were 1.4 million people diagnosed compared to 3.8 million in 2019. And that is set to increase by another 1.2 million in the next 6 years.
Type 2 diabetes is a condition where someone has too much glucose in their blood, and hence the body produces too much insulin that doesn’t work well (to learn more, click here). Many different factors, including our diet, can impact the amount of glucose in our blood. And therefore, it has long been debated what the best diet is for diabetes. Evidence over the years has varied greatly over what diabetics should be eating on a regular basis, confusing people over what they should be doing.
This could be due to the complexity of diabetes and how it affects people in different ways depending on many factors like age, genetic history, and lifestyle choices. Or perhaps, it is due to different studies exploring different things. Also, the fact that the aims of dietary treatment of diabetes differ remains an important factor. For example, it could be to achieve optimal blood glucose levels, to improve energy levels and health, or to prevent or treat diabetes-related complications (to learn more, click here). Throughout this article, we will be looking at a number of different diets looked at in studies to see which one is best for diabetes.
Low fat diet
A low fat diet limits dietary fat intake and relies on carbohydrates, such as bread, rice, potatoes as the main source of energy. In addition to low fat milk and dairy, fruits and vegetables and protein are also similar. Foods like full fat dairy or spreads like butter are usually emitted. This dietary approach is what the UK recommends for the general population as seen in the Eatwell Guide.
A standard low fat diet contains less than 70g per day or less than 30% of total calories. Diabetes UK strongly recommend a low fat approach for people with diabetes. However, relying on carbohydrates can lead to weight gain, insulin resistance, and increased hunger in people trying to manage diabetes (to learn more, click here).
So, why do they recommend it? A low fat dietary approach has been shown to reduce weight and improve glucose intolerance, but not always long term. A study by Swinburn, Metcalf and Ley showed participants following a low fat dietary approach significantly lost some weight initially which also improved glucose tolerance for up to 3 years but was not significantly different at 5 years.
Low/very low carbohydrate diet
A low or very low carbohydrate diet restricts the amount of carbohydrates and instead relies on fats such as full fat dairy and butter as the main source of energy. A low or very low carbohydrate diet is defined differently but the standard low carbohydrate diet contains less than 130g per day or less than 26% of total calorie intake. And a very low carbohydrate diet contains less than 50g per day or less than 10% of total calorie intake.
This type of approach is still considered controversial as limiting carbs is not general guidelines, however, out of all the macro-nutrients it is known that carbohydrates impact blood glucose and insulin levels the most. Low carbohydrate diets usually show a lower HbA1c and less reliance on medication, however it may result in higher cholesterol levels because of the consumption of saturated fat. This diet appears to be superior in weight loss compared to other diets and researchers concluded that using low carbohydrate interventions is effective for improving and reversing type 2 diabetes (to learn more, click here).
Out of all the diets, a Mediterranean diet has always been known as a diet that promotes health and longevity. Similar to other diets, it is defined differently but it tends to contain similar amount of fat and carbohydrates. In comparison to a typical western diet, it has more dietary fat and less refined carbohydrates. It relies on natural, unprocessed wholefoods and good quality protein, wholegrains and vegetables.
A typical Mediterranean diet is rich in olive oil, legumes, unrefined cereals, fruit, and vegetables, low in meat and meat products with moderate contents of dairy products (mostly cheese and yogurt), fish, and wine. It has been shown to aid in weight loss, lower blood glucose levels, and improve cholesterol (to learn more, click here).
Vegan or vegetarian diet
A vegetarian diet avoids meat, poultry, and fish consumption and instead constitutes of cereal products, nuts, seeds, fruit, and vegetables and, occasionally, dairy products or eggs. Whereas vegans avoid dairy products, eggs, or any other foods derived from animals, vegetarians usually do not. These diets have recently become more popular and widespread amongst individuals.
A clinical trial of 22 weeks saw participants that followed a vegan diet reduced their weight, HbA1c, cholesterol levels, and reliance on medication. However, other studies show there isn’t a significant difference following a vegetarian or vegan diet on HbA1c levels, therefore further studies need to be conducted to support the wider use of these diets (to learn more, click here). But it seems the overriding benefits are due to limiting fat from animal products, and increasing fruit and vegetable consumption.
Low GI diet
Glycemic index or GI is defined as a ranking system of carbohydrate foods based on their impact on blood glucose levels. Carbohydrate foods that are broken down quickly by the body and cause a rapid increase in blood glucose levels have a high GI. Low or medium GI foods take a longer time to break down and cause a gradual increase in blood glucose levels over time (to learn more, click here).
A low GI diet will include foods such as lentils, beans, and oats, and limit high-GI foods, such as white bread. This is believed to help minimise fluctuations in blood glucose levels and reduce the secretion of insulin over the day causing the body to become more sensitive to the insulin. However, the glycemic index of food is seen as a secondary step following the total carbohydrate intake as it is rarely considered on its own.
In a meta-analysis by Thomas and Elliot, it was shown that a low GI diet significantly reduced HbA1c to the same extent as certain medication and concluded that is an effective method and should be considered as part of the overall strategy of diabetes management. However, in another study it was also seen that a low GI diet does not have a significant impact on weight loss and the reduction of HbA1c, and might not always be clinically relevant.
This is not a diet that controls macro-nutrient or food quality intake, but rather an eating pattern that cycles between periods of eating and fasting from food. Fasting for long periods allows glucose and insulin levels to reduce which in turn aids the management of diabetes. There are several different methods to implement this fasting into someone’s lifestyle or routine.
The 5:2 diet is one that limits calorie intake between 500-600 for two days in the week or the time-restricted eating where you choose between 4 and 8 hours to eat and the rest of the time is for fasting (to learn more, click here). When fasting, the body is forced to use its stores of fat and glycogen as energy. This in turn may improve blood glucose levels and help with weight loss. A case study saw 3 people injecting insulin try a more extreme version of fasting (24 hour periods), and they were able to cut out the need for insulin treatment altogether after a month of intermittent fasting.
However, the safety of fasting for people with diabetes has been looked into as it has not always been seen to be a safe intervention for those with diabetes. But a pilot study indicated that it is in fact safe and achievable, and also improves weight loss and glucose levels. The evidence around this is growing especially for people who do not want to practice a modest calorie restriction that comes from following a diet everyday.
For each of the diets evaluated above, there seems to be some kind of benefit from that diet even temporarily. But the question remains, what is the best diet for diabetes? Perhaps, there is no one best diet for diabetes and there is no one size that fits all. And rather than labelling it one thing maybe the focus should lie on what all these diets have in common.
The best diet for diabetes will focus on the quality of macro-nutrients like fats and carbohydrates rather than their ratios or their quantities. The diet should aim to be rich in wholegrains, fruits, vegetables, legumes, and nuts, and lower in refined grains, processed meats, and sugary drinks. These overall changes are what have been shown to be effective in improving blood glucose levels and diabetes overall.
Each diet has to be individualised and cultural food preferences need to be taken into account and setting appropriate calorie intake for weight goals (to learn more, click here). This needs to be done with the consultation of a doctor or a diabetic team to help control diabetes in each individual long term.
Key word definitions:
Glucose: a simple sugar that is broken down from carbohydrates and is an important energy source.
Insulin: a hormone produced in the pancreas which regulates the amount of glucose in the blood.
Insulin resistance: an impaired response of the body to insulin, resulting in elevated levels of glucose in the blood.
Macro-nutrients: a type of food (e.g. fat, protein, carbohydrate) required in large amounts in the diet.
HbA1c: your average blood glucose (sugar) levels for the last two to three months.
Cholesterol: a type of fat in the blood called a lipid.
Meta-analysis: an examination of data from a number of independent studies of the same subject, in order to determine overall trends.
Clinical trial: A research study in which one or more human subjects are prospectively assigned to one or more interventions to evaluate the effects on health outcomes.