Written by Diana Licalzi, MS, RD, CDE
Exciting new evidence continues to point to the effectiveness of a plant-based dietary approach for blood sugar control and for the prevention and treatment of type 2 diabetes. As the science becomes more robust, more organizations are recognizing and supporting this way of eating.
In their 2018 guidelines, the American Association of Clinical Endocrinology encouraged their clinicians to recommend a primarily plant-based diet—rich in healthful carbohydrates and low in saturated fats—to their patients with type 2 diabetes. The American Diabetes Association's 2018 Standards of Care also recognized this dietary approach as an effective way to treat type 2 diabetes. And more recently, the American Heart Association stated in their 2021 Dietary Guidance to Improve Cardiovascular Health that the majority of our proteins should be plant-based (people with type 2 diabetes face a 3-5x greater risk of heart disease).
Here’s the latest research on how a plant-based diet can help type 2 diabetes and insulin resistance, how quickly you can expect to see changes in your blood sugar after adopting this dietary approach, and what to do if you experience spikes in your sugar levels as you transition to this new way of eating.
A plant-based diet for type 2 diabetes
Can a plant-based diet improve type 2 diabetes? Countless studies consistently show a link between the intake of plant-based diets and improvements in the course of type 2 diabetes.
One of the most comprehensive studies published to date found solid evidence that adhering to a healthy plant-based diet was associated with a reduced risk of type 2 diabetes. In the systematic review and meta-analysis, researchers examined nine studies that included over 300,000 participants with around 23,000 cases of type 2 diabetes. Those who adhered to a predominantly plant-based diet had a 35% lower risk of type 2 diabetes than those with less adherence. Why do plant-based diets work so well? According to the researchers, healthy plant-based foods like fruits, vegetables, legumes, whole grains, nuts, and seeds have been shown to improve insulin resistance, blood pressure, weight, and inflammation — all factors that may contribute to the development of type 2 diabetes.
Many other studies demonstrate that plant-based diets not only prevent type 2 diabetes but also can treat and reduce the outcomes associated with type 2 diabetes. In 2016, the Canadian Diabetes Association released a comprehensive review of the literature regarding plant-based diets for the treatment of diabetes. They concluded that plant-based diets are “just as effective, if not more effective than other diabetes diets in improving body weight, cardiovascular risk factors, insulin sensitivity, glycated hemoglobin levels, oxidative stress markers, and renovascular markers...and plant-based diets reduced the need for diabetes medications.” This 2019 review also found strong evidence from the meta-analysis of randomized control trials indicating that plant-based diets improve glycemic control by lowering A1c in people with type 2 diabetes.
A plant-based diet for insulin resistance
Evidence points to the effectiveness of plant-based diets in combatting type 2 diabetes because they target insulin resistance — the root cause of type 2 diabetes.
In a large 2018 cohort study, researchers found that a diet higher in plant-based foods and lower in animal-based ones was associated with lower insulin resistance and a lower risk of pre- and type 2 diabetes. The authors concluded that a plant-based diet plays a protective role in the development of type 2 diabetes compared to a more animal-based one. Furthermore, in this randomized control trial, participants were asked to follow a low-fat plant-based diet or to make no changes to their diet for 16 weeks. Participants who followed the low-fat plant-based diet had significantly improved insulin resistance and beta-cell (pancreatic) function.
On the other hand, a study conducted by Azemati and colleagues in 2017 aimed to determine the association between protein intake and its link to insulin resistance. Their results showed that the long-term effects of a higher total protein and higher animal protein were both associated with increased insulin resistance. To further expand on this point, a 2015 meta-analysis examined the meat intake of over 50,000 people. They found that the consumption of meat was associated with higher fasting glucose levels and higher fasting insulin concentration. One explanation for this outcome is due to red meat's high content of saturated fat. When examining saturated fat specifically, its high intake may also increase one’s risk of developing type 2 diabetes.
I’m eating a plant-based or vegan diet but experiencing high blood sugar
It’s not uncommon to experience blood sugar spikes after first adopting a plant-based diet. To grasp this phenomenon, it is important to understand the normal metabolism of carbohydrates.
Glucose normally fluctuates throughout the day, particularly after meals. When we consume carbohydrates, our body breaks them down and converts them into glucose. When glucose enters our bloodstream, the pancreas receives a signal to release a hormone called insulin. As you can see below, insulin acts as a "key,” allowing glucose to funnel out of the bloodstream and into our cells. As this process continues, blood glucose levels drop back down.
Research demonstrates that insulin resistance develops from a continuous surplus of calories (aka energy) entering the body. Evolutionarily, our bodies were not programmed to waste energy so any food we consume is either used right away or stored as fat for later use. Our bodies, though, contain a finite number of adipose (fat cells), and there is a limit as to how much fat they can hold. Thus, as our cells store more and more fat, they begin to reach their capacity, causing them to swell up and produce an inflammatory response. This response shuts off the insulin receptors on the cells. As more insulin receptors shut off, less glucose can enter the cell leaving an individual with high blood sugar.
As insulin resistance worsens, so does our body’s ability to use and metabolize carbohydrates properly. Glucose spikes after a meal indicate you likely have poor carbohydrate tolerance due to insulin resistance. For this reason, when you eat a healthy carbohydrate, like an apple, you may experience a glucose spike. A slow transition away from a diet high in animal food sources (and processed foods!) is one of the best ways to reverse insulin resistance and improve your carbohydrate tolerance. For quick and easy plant-based meal ideas, check out this blog.
How long does it take a vegan or plant-based diet to lower blood sugar?
It can take two weeks up to a few months to see lower blood sugar after adopting a vegan or plant-based diet. Because many studies focus on long-term results, we don’t have a lot of research measuring the short-term effects of a plant-based diet on blood sugar levels.
In a trial of a low-fat vegan diet in individuals with type 2 diabetes, participants experienced a 28% reduction in their glucose levels (195 to 141 mg/dl) after 12 weeks. In this 2016 study, participants who adhered to a low-fat, plant-based diet saw an average drop of 21 points in their fasting blood glucose in as few as four weeks. And although these are just case studies, participants who adhere strictly to the Reversing T2D’s low saturated fat, plant-based diet see improvements in their glucose levels as in a few as two weeks.
Ultimately, changes in your blood sugar are determined by two main factors, (1) your level of insulin resistance, (2) and how aggressive you are with your dietary and lifestyle changes. For example, if you have been diagnosed with pre-diabetes (which indicates a lower level of insulin resistance) and adhere to a strictly plant-based diet and incorporate exercise, there is a good chance you’ll see quicker improvements in your blood sugar.
To recap the evidence behind plant-based diets and blood sugar:
- Countless studies consistently show a link between the adoption of a plant-based diet and improvements in the course of type 2 diabetes.
- Plant-based proteins work by preventing and reversing insulin resistance while animal-based ones contribute to its development.
- You may experience blood sugar spikes after starting a vegan or plant-based diet because of your insulin resistance and poor carbohydrate tolerance. Perseverance is important during this stage; continue a plant-based diet and you will see improvements.
- It can take anywhere from two weeks to a few months to see reductions in your blood sugar after starting a vegan or plant-based diet.