Updated 6th September 2023

Can polyphenols help tackle type 2 diabetes?

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Type 2 diabetes is a huge and growing concern.

Worldwide, a staggering 422 million people have type 2 diabetes. And it causes 1.5 million deaths each year.

Currently, this metabolic condition affects about 1 in 10 people in the United States and around 1 in 10 people over 40 in the United Kingdom. 

Experts have already uncovered some major risk factors: An estimated 90% of type 2 diabetes cases are attributed to physical inactivity, smoking, overweight or obesity, alcohol consumption, and diet.

Diet and diabetes

Studies have repeatedly found that having a plant-based diet, like the Mediterranean diet, can help prevent and even treat type 2 diabetes

Dietary patterns are complex — we eat many different foods every week, each containing tens or hundreds of compounds. 

Still, we know that a healthy, plant-based diet probably decreases your risk of developing type 2 diabetes in several ways.

And some scientists are particularly interested in the role of plant compounds called polyphenols.

Before we dive into these fascinating chemicals, let’s do a quick refresher on type 2 diabetes.

Type 2 diabetes in brief

After you eat, your gut breaks down digestible carbs into simple sugars, like glucose. 

These simple sugars move through the wall of your gut and into your blood. Thus, the level of sugar in your blood naturally rises — this is normal.

Your blood then carries this sugar around your body to be used or stored.

Although blood sugar is essential to keep you alive, you can have too much of a good thing.

If your blood sugar level rises sharply or stays elevated for a long time, it can start to damage organs and tissues.

To keep your blood sugar level in check, your body produces insulin after you eat. This hormone helps remove sugar from your blood. So, as your insulin level rises, your blood sugar level drops.

If you have type 2 diabetes, either you don’t produce enough insulin or your insulin receptors are less sensitive.

With this reduced sensitivity, insulin is less effective at moving sugar away from your blood. 

In short, people with type 2 diabetes produce less insulin, their insulin is less effective, or both. So, overall, their blood sugar levels tend to be too high.

Now, back to plant compounds.

What are polyphenols?

Polyphenols are produced by a wide range of plants. They help protect the plant from damage caused by ultraviolet light and ward off hungry microbes.

They’re particularly common in vegetables, fruits, whole grains, and legumes. Cocoa, coffee, tea, spices, and red wine are also rich in polyphenols.

Scientists have identified more than 8,000 polyphenols in plants. 

Experts divide polyphenols into four groups: flavonoids, phenolic acids, stilbenes, and lignans.

The most common polyphenols in your diet are flavonoids, which include flavones, flavonols, flavanols, flavanones, isoflavones, and anthocyanins. 

But let’s not get bogged down by a bunch of similar-sounding names. 

The important point is: There are loads of polyphenols, and if you eat a variety of plants, you eat a lot of these chemicals. But do they reduce your risk of type 2 diabetes?

What’s the evidence?

Many studies have spotted associations between polyphenol intake and type 2 diabetes risk.

We’ll cover three fairly large studies here.

Spanish study

One study included data from 3,430 older adults without diabetes but with a high risk of cardiovascular disease. 

The authors concluded that those who consumed the most polyphenols were 28% less likely to develop type 2 diabetes than those who ate the least polyphenols.

Korean study

This study included data from 7,963 women in Korea. Among them, 225 had type 2 diabetes. 

The scientists found that the intake of polyphenols called anthocyanidins and flavones was significantly lower in those with type 2 diabetes.

Chinese study

This research focused on a polyphenol called quercetin. The researchers showed that the more quercetin an individual consumed, the lower their odds of having type 2 diabetes.

Meanwhile, similar studies have also found links between polyphenol consumption and diabetes risk.

But we need to be cautious. There are pitfalls aplenty with this kind of research.

Some notes of caution

The studies outlined above only show associations — they don’t prove that polyphenols cause a reduced risk of diabetes.

Also, plants contain a wide range of compounds, and it’s possible that some other nutrient is driving the association.

Or, it might be that if you eat more plants, you eat fewer unhealthy foods in general or you're more physically active.

Although scientists try to account for some of these factors in their analyses, they're tricky to pin down.

Also, not all studies have linked dietary polyphenols and type 2 diabetes risk.

The authors of a review suggest that this might be partly because measuring polyphenol intake is fairly imprecise

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One problem is that you rely on people to give you accurate information about their diets. And human memories aren’t perfect.

Another challenge is that polyphenol levels can vary considerably. For instance, organic fruits sometimes have higher levels of polyphenols than nonorganic fruits. 

Other factors, like rainfall, sun exposure, and how food is stored and prepared can also alter a food's polyphenol levels.

And the amount of polyphenols can even vary within the same fruit or vegetable — for instance, levels can differ between a fruit’s peel and its pulp. 

To draw a clearer picture, we need to look at data from closely controlled clinical trials.

Evidence from clinical trials

Above, we outlined epidemiological studies that included large numbers of people. These are important in helping scientists spot patterns and associations.

Then, scientists run smaller, more tightly controlled studies to understand whether those associations are causal. These are clinical trials. Let’s look at a couple.

8-week study

One 8-week clinical trial examined links between polyphenols, omega-3s, and blood sugar control.

The researchers recruited 86 participants with overweight or obesity and assigned them to four groups. Each followed a different diet, some of which were rich in polyphenols.

At the beginning and end of the study, the scientists gave the participants a test meal and measured their blood sugar responses.

At the end of the study, participants with the high-polyphenol diets had significantly reduced blood sugar responses.

Acacia polyphenols

Another clinical trial tested polyphenols extracted from a species of acacia plant. 

The scientists recruited 34 people with prediabetes. People with prediabetes have higher than usual blood sugar levels, but these are still too low for a diagnosis of type 2 diabetes.

Having prediabetes means that you have a higher risk of developing the condition.

Half the participants took an acacia polyphenol supplement each day for 8 weeks, and the other half took a placebo.

The team found that participants taking the polyphenol supplement had significantly reduced blood sugar responses to a meal at the end of the study, compared with the beginning. This wasn't true for the people who took the placebo.

By now, several clinical trials have measured the positive effects of polyphenols on blood sugar control. So, the next question is …

How do polyphenols influence blood sugar?

If these wonderful plant compounds really do influence blood sugar control and protect against type 2 diabetes, how are they doing it?

Evidence suggests that polyphenols probably work their magic via a number of routes. So, let’s get into the science.

Slowing glucose absorption

Large carbohydrate molecules can’t travel through the walls of your gut. Enzymes need to snip them into simple sugars, like glucose, before they can enter your blood. 

Polyphenols slow this process by inhibiting some of the carb-snipping enzymes.

Once carbs have been chopped up into glucose, they move through your gut lining using glucose transporters.

Polyphenols may also interact with these transporters, slowing the movement of glucose from your gut to your blood. 

So, polyphenols seem to hinder the breakdown of larger carb molecules and slow their passage into your blood. 

Both of these actions will reduce your blood sugar response after a meal.

Increasing glucose uptake

Evidence from lab and animal studies suggests that polyphenols can help your body remove glucose from your blood more quickly. 

It might do this by increasing your insulin sensitivity, which means that glucose is more efficiently shunted out of your blood.

Also, lab studies suggest that polyphenols can increase the number or sensitivity of glucose transporters on muscles. This means that glucose is moved from your blood into your muscles more efficiently.

A role for gut bacteria

An estimated 90–95% of the polyphenols you consume aren’t absorbed through your gut lining. Instead, they reach your large intestine, where they feed your gut bacteria and keep them happy.

Some evidence suggests that polyphenols might increase numbers of Bifidobacteria in your gut.

And increased numbers of Bifidobacteria seem to be associated with better blood sugar control

The full story of how gut bacteria are involved is yet to be told. And it’s likely to be incredibly complicated.

Wrapping up

Scientists are still digging into the links between polyphenols, blood sugar control, and type 2 diabetes. 

But evidence is mounting that these plant compounds can positively influence your blood sugar control and may reduce your type 2 diabetes risk.

The authors of one review concluded that “The intake of polyphenols may be beneficial for both insulin resistance and [type 2 diabetes] risk.”

According to another review, “Abundant epidemiologic studies [prove] the constructive effect of polyphenol-rich diet on [type 2 diabetes].” 

In agreement, another review reads: “This study adds to the evidence showing that diets rich in polyphenols, and particularly flavonoids, play a role in the prevention of type 2 diabetes.”

What should you do?

As researchers continue to uncover the link between these plant chemicals and the risk of developing type 2 diabetes, upping your polyphenol intake is a safe bet.

Aside from blood sugar control, polyphenols may also protect heart, gut, and skin health.

And there’s some evidence that they could reduce your risk of developing cancer and boost your cognitive performance.

Scientists are still unraveling the roles that polyphenols play in our health. And much of what we’ve discussed here is still being investigated.

 But because plant foods that are good for your health contain high levels of polyphenols, increasing your intake of these plants will likely benefit you. 

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