How Intermittent Fasting Affects Diabetes & Blood Sugar

The central reason why people get type 2 diabetes is insulin resistance. This is when your cells lose their ability to respond to a really important hormone called insulin. Diabetes affects millions of people worldwide and often starts years before symptoms are obvious and a diagnosis is made. 

This article explains how intermittent fasting can affect your blood sugar levels, insulin levels and your diabetes risk. We’ll also cover what the evidence shows and how to use intermittent fasting to manage it.

Type 2 diabetes doesn’t appear overnight; it is a “progressive” disease as your cells’ resistance to insulin slowly and quietly gets worse over time. This is important because it means there is a long window, giving us time to fix it before it becomes irreparable. It seems that intermittent fasting can alter the trajectory of the disease, with a strong body of evidence behind it.

Insulin, glucose and how things go wrong

When you eat carbohydrate you digestive system breaks them down into sugar (otherwise known as 'glucose'). Glucose then enters your blood (which is where it's measured). After it enters your blood, your pancreas reacts and starts releasing insulin, whose main job is to tell your cells to let glucose into them.

Your body doesn’t like too much glucose in your bloodstream. So when glucose increases (after you eat), it needs to get rid of it. So it either directs it to your cells to burn for energy, or it stores it in your liver or muscles (as 'glycogen') or in fat tissue (as fat).

In a normal, healthy body, this works seamlessly. But if your cells are "insulin-resistant" (usually because they’ve been exposed to too much insulin or you’re too inactive), your body has to store the excess glucose somewhere. 

What it does is pack it into your fat cells, your organs and any cells that will take it, and it just remains in your blood as well. This isn’t good; it is a temporary solution that actually makes the insulin resistance worse! And if it carries on like this, you’ll end up with type 2 diabetes. Insulin resistance is also associated with other diseases like polycystic ovary syndrome, liver diseases, obesity, and blood vessel diseases.^[1]

How intermittent fasting helps control blood sugar

When you eat, particularly carbohydrate-rich foods, glucose and insulin increase for a couple of hours in a normal, healthy person. And if you fast for long enough, your glucose and insulin levels will then drop. 

So if you’re eating a typical three-meals-a-day-plus-snacks, your glucose and insulin levels stay elevated for most of the day. So your cells are consistently exposed to insulin during this time, day in, day out.

Fasting for a sustained period throughout the day allows your insulin levels to drop and gives your cells a break (both the ones that produce insulin and respond to it). This break seems to make them more “sensitive” to insulin, meaning your pancreas doesn’t need to produce as much insulin in the first place.^[2]

Intermittent fasting does help with weight loss and fat loss. It can also help lower insulin resistance, reduce strain on your insulin-producing cells, and decrease diabetes risk, even if you don't lose any body weight. So you get double benefits, as it can improve your metabolic health directly and help you lose excess body weight.^[3]

Visceral fat

In addition to general weight loss and fat loss that comes with intermittent fasting, it is also effective at targeting a specific type of fat: “visceral fat”, which is stored around your organs and abdomen, and is really unhealthy. Having too much visceral fat causes inflammation, worsens insulin resistance, and is linked to several other diseases.^[4]

Liver function

Your pancreas (insulin-producing organ) gets all the attention when it comes to diabetes and managing your blood sugar levels. However, your liver is also really important as well. 

Just like eating carbohydrates increases your blood glucose and insulin levels, your liver can also increase your glucose levels by dumping its stored glucose into your bloodstream. Insulin is supposed to stop your liver from doing this. 

But if your liver cells are insulin-resistant, it ignores this signal. Intermittent fasting can help correct this by reducing the workload on your liver, your liver fat, and potentially improving its insulin sensitivity. This stops it from dumping glucose into your bloodstream when it doesn’t need to.^[5]

Circadian rhythm

Your body tends to handle glucose better in the morning and afternoon than in the evening. So, eating whilst your body can handle glucose better (rather than later in the day) will lower the strain on your body, as it doesn’t have to work as hard to achieve the same results.

This is why early time-restricted eating (eating between 7-8 pm to 3-4 pm) appears to outperform late time-restricted windows, even when calorie and macronutrient intake is the same.^[6]

Intermittent fasting and diabetes risk

So intermittent fasting positively affects blood sugar and insulin levels pretty consistently, and it also seems to reduce type 2 diabetes risk.

A few months of intermittent fasting is shown to improve diabetes markers and medication requirements in people with type 2 diabetes, which are comparable to the effects of some glucose-lowering medications.^[7] 

In people with “prediabetes” (at risk of diabetes), six months of intermittent fasting improves blood sugar control better than those who were following a standard calorie-restricted diet.^[8] 

In healthy people with no diagnosed metabolic health problems, there are still improvements in some health markers, but they tend to be more modest. So the overall picture is that the worse the person's health, the more profound the effects of intermittent fasting seem to be.^[4] 

What type of intermittent fasting works best?

Early time-restricted eating (finishing the eating window by late afternoon) seems to be better than late-night eating windows. Ten-hour and eight-hour time-restricted intermittent fasting eating windows have both been shown to be effective at improving diabetes risk. 

Likewise, there is also evidence showing that periodic intermittent fasting, like the 5:2 or alternate-day eating pattern, is effective. However, in our opinion, the longer, more demanding fasting protocols are less desirable as there is no consistent daily pattern, blood glucose fluctuations are greater, and some people find them more difficult to follow.^[9]

Putting the Theory into Practice