Blood glucose levels increase after eating and return to baseline within a few hours. The amount by which blood glucose rises after eating is largely determined by meal composition, prior physical activity, and the time of day because glucose tolerance (i.e., how well the body resists spikes in blood glucose after eating) peaks in the morning and declines in the afternoon and evening.^[13] Glucose tolerance also tends to decline with age.^[14]

Lifestyle changes can lead to a remission of type 2 diabetes. Following specific diets (e.g., low-carb, vegan, fasting) probably isn’t that important, so long as the chosen eating plan facilitates a sustained, moderate calorie deficit that results in weight loss (sometimes as little as 5%–10% of original body weight) and a reduction in intra-organ fat.^[15][16][17] In fact, given that weight loss and maintenance is so challenging, people who are seeking to improve their type 2 diabetes with weight loss should simply focus on dietary patterns that are realistic, sustainable, and as mentally and emotionally healthy as possible. Even if weight loss isn’t attainable, physical activity alone can improve some key measures of type 2 diabetes, such as HbA1c.^[18] That said, these benefits are still most pronounced when there’s a simultaneous increase in physical activity and decrease in body weight.^[19]

The main cause of type 2 diabetes is excess fat accumulation in the liver and pancreas, which leads to insulin resistance and inadequate insulin production.^[20] Consequently, people with overweight or obesity are at an increased risk of type 2 diabetes, especially if they have an upper body and visceral fat storage pattern.^[21]

Type 1 diabetes, formerly called juvenile diabetes, is ultimately an autoimmune disease, though it is often heritable and influenced by multiple genes,^[22] with the highest incidences reported in Finland and other Northern European nations.^[23] Environmental triggers, such as exposure to certain viruses (e.g., enterovirus) and nutritional factors, may also increase the risk of type 1 diabetes.^[24] The reason why some people develop type 1 diabetes is not fully known, but the evidence is at least clear that it is caused by autoimmune destruction of the beta cells, often after a viral infection.

When blood sugar levels are chronically elevated due to uncontrolled diabetes, red blood cells are exposed to high levels of glucose molecules. Glucose in the bloodstream will irreversibly attach itself to hemoglobin molecules at levels substantially higher than in blood without elevated blood sugar.

The percentage of these “glycated” hemoglobin molecules can be measured, and the levels are used to assess how well an individual is managing their disease and whether they are at an increased risk for cardiovascular complications.

HbA1c can be used to measure disease state. The “Hb” stands for hemoglobin, and the “A1c” is simply the type of hemoglobin that glucose attaches to. Ninety percent of hemoglobin is the “A” or “Adult” type, and “A1c” is one of the minor components of hemoglobin, which also includes A1b, A1a1, and A1a2. The key reason why HbA1c is a better marker than glucose for chronic exposure is that blood glucose is very transient, whereas the half life of HbA1c is about 3 months. Although HbA1c is indicative of longer-term blood sugar levels up to 3 or more months, it is likely somewhat more weighted toward blood sugar levels during the previous 2 to 4 weeks.

There are many ways^[25] to measure insulin resistance. The gold standard is the euglycemic hyperinsulinemic clamp. In this technique, insulin is infused into a vein to reach a constant level in the blood. Because insulin is being pumped into the blood, the person has artificially high insulin, or hyperinsulinemia. Simultaneously, glucose is also infused at a varying rate until the blood glucose level stabilizes at a normal level. When a person’s blood glucose is normal, it is called euglycemia (the Greek root “eu-” means “good”). At this point, the rate of glucose infusion exactly equals the amount being taken up by the body’s tissues, which is a direct measure of insulin sensitivity. The more glucose that has to be infused to maintain euglycemia, the more it’s being taken up, meaning the tissue is more sensitive to insulin.

The problem with this technique is that it takes a couple of hours to complete and is relatively expensive. In response, lower cost and easier to use methods of estimating insulin resistance have been developed. Two major methods are HOMA-IR and QUICKI. Both require only a single blood draw in order to measure fasting glucose and C-peptide, a byproduct of insulin synthesis. These values are then plugged into an equation that estimates insulin sensitivity. However, these estimations aren’t perfect.

Long term complications of type 1 and type 2 diabetes include the following:

• Heart disease
• Stroke
• Blindness
• Kidney failure requiring dialysis
• Peripheral vascular disease leading to limb amputation
• Dementia
• Nerve damage

What is insulin sensitivity?

Definitions

Insulin sensitivity is a general phenomena in the body, and can be measured a few ways through studies.

The pancreas (an organ that regulates blood sugar) secretes insulin in response to high blood sugar, and cells (like muscle or fat cells) can absorb blood sugar when stimulated by insulin.

Insulin sensitivity is the relationship between how much insulin needs to be produced in order to deposit a certain amount of glucose. You are insulin sensitive if a small amount of insulin needs to be secreted to deposit a certain amount of glucose, and insulin resistant if a lot of insulin needs to be secreted to deposit the same amount of glucose.

Insulin sensitivity is seen as good as the opposite, insulin resistance, is a major risk factor for the development of Type II diabetes.

Types of Insulin Sensitivity

There are three main types of insulin sensitivity; peripheral insulin sensitivity, hepatic insulin sensitivity, and pancreatic insulin sensitivity.

Peripheral insulin sensitivity is how readily body cells in your periphery tissue, such as muscle and fat, can absorb glucose; either on their own (muscle can absorb glucose when contracted) or when insulin stimulates them. It is the most well-known form of insulin resistance.

Hepatic insulin sensitivity is related to the process of gluconeogenesis, the production of new blood sugar. Usually inflammatory factors prevent insulin from acting in the liver via inducing insulin resistance, and insulin's actions are unable to tell the liver to 'stop' producing glucose.^[26][27]

Pancreatic insulin sensitivity is the functioning of the cells that secrete insulin, the beta-cells. If these are damaged or cannot function, insulin resistance can develop. This is more of a concern in disease states like Type I diabetes (insulin insufficiency)^[28][29] or Cystic Fibrosis (where the function in physically hindered).^[30]

Insulin sensitivity is how effective the body is as using insulin to reduce elevated blood glucose levels, with a greater efficacy being more 'sensitivity' and poorer efficacy being more 'resistant'. When the body becomes too poor at using insulin to reduce blood glucose levels, type II diabetes ensues

Lifestyle

Non-modifiable factors

It seems that insulin sensitivity is negatively associated with age^[31] although these may be related more to lifestyle than to age per se.^[32] The ability to reverse insulin resistance with exercise does not appear to be different between young and old.^[31] Exercise tends to be recommended to older individuals to improve glucose metabolism.^[33]

Modifiable factors

There is an association with obesity and insulin resistance, with insulin resistant individuals usually having more body fat. However, this also appears to be lifestyle related as increases in insulin sensitivity can occur without weight loss.^[34] Some studies do note more drastic benefits in insulin sensitization in obese individuals, which is probably due to worse baseline statistics.^[34]

Exercise

Aerobic Exercise (Ex. Jogging)

Aerobic exercise, or exercise that you can maintain for a prolonged period of time, seems to be able to acutely improve insulin resistance by increasing uptake of glucose into cells. It can increase insulin sensitivity immediately, as a session of 25-60 minutes (at 60-95% VO₂ max) for 3-5 days.^[35] Improvements can also be seen after a week of aerobic training, when doing mostly 2 short sessions of 25 minutes of walking at 70% VO₂ max.^[36] Interestingly, the opposite is also true. Voluntary restriction of activity or a drastic increase in sedentary activity can reduce insulin sensitivity in as little as 2 weeks.^[37]

Over the long term, aerboic exercise done routinely can preseve beneficial changes in insulin sensitivity.^[38]

Insulin sensitivity as a result of exercise can occur independent of weight loss.^[34][39] This is not to say that aerobic exercise will not lead to weight loss, as it may.^[40] The function of weight loss seems to be a blend of activity and diet, whereas insulin sensitivity increases could occur without changes in the diet.

In regards to hepatic insulin resistance, it has been seen over time periods of 12 weeks light aerobic activity^[41][34] but studies lasting 1 week have sometimes noted no difference.^[36]

Anaerobic Exercise (Ex. Weightlifting)

Strength exercises (lifting weights usually) is also associated with increasing insulin sensitivity as well as increased muscle mass.^[42]

In persons with impaired glucose tolerance, more sets of an exercise tend to be more effective than single sets and higher intensities better than moderate.^[43]

The general idea of exercise is that you want to have lean (muscle) mass, and you want it to contract somewhat regularly so it can take up glucose. The more properly functioning muscle mass one has, the better peripheral insulin sensitivity is

Supplementation

Supplements may be either supplements that directly act upon cells to induce insulin sensitizing effects (like resveratrol or carnitine) or may inhibit or otherwise delay carbohydrate uptake (like green tea catechins and perhaps chlorogenic acid)

Using some of these compounds in conjunction with diet/exercise techniques conducive to regaining insulin sensitivity would be advisable.

The most commonly used insoluble fiber supplement is wheat fiber. However, it hasn’t been studied enough under well-controlled conditions for researchers to have a full understanding of its effects, and the existing body of research does not clearly support its use for blood sugar management.^[8][9][10] The same goes for studies on isolated arabinoxylan, the dominant form of fiber in wheat.^[11][12]

Although we hate the term "superfood" with a fury only possible from a team of nutrition researchers, some foods happen to have health benefits that are backed up by randomized trials in humans. One such food is the humble blueberry, which can be seen at the bottom of the phytochemical family tree below:

But .... did you know that blueberries might also help with blood sugar regulation? Which is a bit strange, since blueberries contain sugar, to the tune of 15 grams of sugar per cup of blueberries. So how is it that a sugary fruit can help with blood sugar? Well, maybe you’re a skeptic (which is an incredibly helpful trait for a nutrition researcher, so nice job!), and you’re thinking “15 grams isn’t that much sugar, especially when a cup of blueberries also has almost 4 grams of fiber”.

Correct! But let me present Exhibit B: The mango. A cup of mango chunks contains 23 grams of sugar, and only 2.6 grams of fiber. And as any mango connoisseur knows, some varieties are pulpier with more fiber, and some have very little fiber and more delicious creaminess.

So you might be surprised to find that twelve weeks of mango consumption reduced blood sugar in a randomized trial. Not only that, the mango didn’t even come in the form of whole fruit, but rather in a quickly digested freeze-dried powder form (which would not be the choice of glycemic index adherents … RIP glycemic index usefulness).

How in the heck is it possible for a sugary fruit to reduce blood sugar? It’s those ol’ phytochemicals again. Specifically, mangos contain a phytochemical called mangiferin, which may help slow absorption of carbohydrates in the intestine. But researchers don’t fully understand how mango phytochemicals do their thing, or even which phytochemicals are involved.

Fruits such as blueberry and mango may help with blood sugar regulation, even though they contain sugar. They may not have very strong effects like medications do, at least in isolation, but a diet rich in different plants may compound the benefits of any one single plant food.

Many people find fruit to be delicious. It turns out that delicious fruit is often quite healthy. Aside from mango, aptly dubbed “The King of Fruits”, other delicious fruits (such as pomegranate) are also theoretically linked to improved blood sugar regulation.

Don’t be scared of the moderate amounts of fructose in fruit, based only on isolated animal studies. For further reading, check out our analysis of fructose versus glucose versus HFCS of a recent human trial.