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Preventing and treating illness

November 29, 2019

Is there a diet that can prevent or manage diabetes?

You’ve heard of diets like low-carb, keto and intermittent fasting. But can any of them help with diabetes?

Did you know that one in three people in Canada are living with either diabetes or pre-diabetes1? According to Statistics Canada, roughly 2.3 million Canadians age 12 and older reported being diagnosed with diabetes.

But what can we do to stop diabetes in its tracks? Our diets or eating habits may play a contributing role, suggests Medical Director Dr. Paul Oh and Registered Dietitian Niloufar Deilami (RD, MPH).

Dr. Oh and Niloufar both work at the Cardiovascular Prevention and Rehabilitation Program at the University Health Network. Together, they’ve poured through studies that look at which diets and healthy-eating habits can help reduce the risk of diabetes. And, how recently popular diets (like keto and intermittent fasting) can affect blood sugar levels.  

But before we dive into their findings, let’s look at what diabetes is and how it affects people.

What is Type 1 diabetes, Type 2 diabetes and prediabetes?

Type 1 diabetes happens when the body is no longer able to make insulin because the immune system has destroyed the cells that make it. Unfortunately, Type 1 diabetes is not preventable. Being overweight or inactive doesn’t cause it. It’s often treated with insulin injections, along with a healthy diet low in carbohydrates, and exercise.

Type 2 diabetes happens when the pancreas fails to produce insulin or the body does not process the hormone effectively.

Prediabetes happens when blood glucose is abnormally high, but not quite at the diabetic level. It can be reversible in some cases.

Both prediabetes and Type 2 diabetes are conditions that can be prevented and managed by following a healthy lifestyle.

Dr. Oh and Niloufar emphasize that nutrition is one of the key risk factors for diabetes and choosing a healthy eating pattern can reduce the risk of developing pre-diabetes, diabetes and complications of diabetes. Based on the studies listed below, here’s what researchers have learned about diets and eating habits, and how it affects people who have or are at risk of diabetes:

Is there a diet that can help prevent diabetes?

There’s no special “diabetes prevention diet.” But there are dietary patterns that can help reduce the risk of developing diabetes. These patterns include the low glycemic index diets, Mediterranean Diet, the DASH diet, vegetarian diets and the portfolio diet.2 These dietary patterns not only help with diabetes prevention, but can also reduce the risk of heart disease and stroke. 

While these dietary patterns are all slightly unique, they have a few factors in common. All of the diets listed above are mostly plant-based. This means that they include a variety of fruits, vegetables, whole grains, nuts and seeds, and legumes. These dietary patterns also recommend including more whole and unprocessed foods and less highly processed foods.

Canada’s new Food Guide3 can help you achieve this healthy way of eating. The Food Guide promotes having:

  • 1/2 a plate of vegetables and fruit
  • 1/4 plate of whole grains such as brown rice, whole grain pasta, breads and cereal, barley and whole grain oats
  • 1/4 plate of protein with an emphasis on plant proteins including nuts and seeds, legumes and soy protein

What’s the best diet for managing diabetes after it’s diagnosed?

The dietary patterns that help prevent diabetes can also help with diabetes management. How? Research shows that these patterns can help lower blood sugar levels and reduce the risk of complications.2 Low glycemic index carbohydrates raise your blood sugar less compared to  those that have a higher glycemic index. Carbohydrates that have a lower glycemic index include sweet potatoes, barley, brown rice, whole grain oats, and whole grain cereals. Higher glycemic index foods include processed grains such as white bread, white rice, white potatoes and low fibre cereals.

Are you living with diabetes? Measuring your blood sugars at home can help determine the right type and amount of carbohydrates you can tolerate.  A registered dietitian can help you interpret your blood sugar numbers and make suggestions on what changes you can make to your diet to improve your diabetes management.

Can low carb, keto and intermittent fasting diets help prevent or manage diabetes?

Low carbohydrate, very low carbohydrate (the ketogenic diet) and intermittent fasting diets have become popular among the public. But please note that there’s some controversy around these diets. Here’s what you need to know:  

What’s a low carb or keto diet? A low carbohydrate diet consists of no more than 130 grams of carbohydrate per day.4 The ketogenic (keto) diet is a very low-carb diet and allows no more than 50 grams of carbohydrate per day.4 This involves a strict elimination of all carbohydrate-containing foods including fruits, grains, legumes, starchy vegetables and dairy products.

Some studies show that low carbohydrate and ketogenic diets may help lower blood sugar levels and promote weight loss.4  But in a report titled “The Ketogenic Diet for Obesity and Diabetes—Enthusiasm Outpaces Evidence,” researchers noted that most of these studies usually only last for 12 months. And study participants often receive a lot of support and guidance to follow these diets, which may not be realistic in the real world.5  For example, not everyone may have access to see a dietitian on a regular basis.

What are the risks of a low-carb or keto diet? Some of the potential short terms risks of the keto diet include:

  • fatigue,
  • flu-like symptoms,
  • constipation,
  • nutrient deficiencies, and
  • bad breath.

Long-term risks of these diets are yet to be studied. You must also keep in mind that these low-carb diets eliminate a lot of healthy dietary fibre that can help reduce the risk of diabetes, heart disease and some cancers.

What’s intermittent fasting? Intermittent fasting diets have also become increasingly popular. It include various meal-timing schedules where people choose to fast (or not eat) for certain periods of time. Popular fasting methods include:

  • 16:8 (daily 16-hour fast),
  • 5:2 (fast 2 times per week) and
  • Alternate Day Fasting (fast every other day).

What are the pros and cons of intermittent fasting? Studies done on intermittent fasting also show potential reductions in blood sugar and weight loss that are comparable to the effects of eating less every day.6,7,8  But looking through the evidence, it appears that most of the studies are short-term and last up to 1 year and include a small number of participants.7,8  More research needs to be done to determine whether intermittent fasting is a practical alternative to other healthy-eating patterns. Similar to low-carb diets, these diets can also be challenging to follow for long period of time or indefinitely.

What’s more, these diets may not be safe for people taking certain medications. If you’re living with diabetes, always consult with your doctor or dietitian before making any changes to your diet.  

Create a healthy-eating plan for preventing or managing diabetes

A healthy, well-balanced diet that’s enjoyable and includes a variety of whole, unprocessed and plant-based foods can help with the prevention and management of diabetes. Remember, a healthy-eating pattern isn’t one that’s trendy. It’s one that aligns with your personal values, culture and preferences and can be sustainable in the long term.

More on preventing and managing diabetes:

1 Diabetes Canada. (2019). Charter Backgrounders. Retrieved from
2 Diabetes Canada. (2018). Chapter 11: Nutrition Therapy. Retrieved from http://guidelines.diabetes.ca/cpg/chapter11
3 Canada’s food guide. (2019, October 11). Retrieved from https://food-guide.canada.ca/en/
4 Kirkpatrick, C. F., Bolick, J. P., Etherton, P. K., Sikand, G., Aspry, K. E., Soffer, D. E., … Willard, K. E. (2019). Review of current evidence and clinical recommendations on the effects of low-carbohydrate and very-low-carbohydrate (including ketogenic) diets for the management of body weight and other cardiometabolic risk factors: A scientific statement from the National Lipid Association Nutrition and Lifestyle Task Force. Journal of Clinical Lipidology0(0).
5 Joshi, S., Ostfeld, R. J., & McMacken, M. (2019). The Ketogenic Diet for Obesity and Diabetes—Enthusiasm Outpaces Evidence. JAMA Internal Medicine179(9), 1163. doi:10.1001/jamainternmed.2019.2633
6 Barnosky, A. R., Hoddy, K. K., Unterman, T. G., & Varady, K. A. (2014). Intermittent fasting vs daily calorie restriction for type 2 diabetes prevention: a review of human findings. Translational Research164(4), 302-311. doi:10.1016/j.trsl.2014.05.013
7Furmli, S., Elmasry, R., Ramos, M., & Fung, J. (2018). Therapeutic use of intermittent fasting for people with type 2 diabetes as an alternative to insulin. BMJ Case Reports, bcr-2017-221854. doi:10.1136/bcr-2017-221854
8 Papamichou, D., Panagiotakos, D., & Itsiopoulos, C. (2019). Dietary patterns and management of type 2 diabetes: A systematic review of randomised clinical trials. Nutrition, Metabolism and Cardiovascular Diseases29(6), 531-543. doi:10.1016/j.numecd.2019.02.004

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