Understanding Metabolic Flexibilty and the Role of Insulin

What is Metabolic Flexibility?

Metabolic flexibility refers to the ability of your body to adapt to changes in diet and exercise. Your body has the capability to change its metabolism depending on what it needs at any given time. If you are under stress or have a chronic illness, then your metabolism may slow down temporarily. However, if you do not need energy from food, then your metabolism will increase rapidly due to increased fat burning (metabolism).

Your body’s metabolism is determined by several factors: genetics, age, gender, activity level, physical condition (body composition), hormones such as thyroid hormone and growth factor levels, and environmental factors like nutrition. These factors all affect your metabolic rate.

When you eat less than your daily caloric requirement (calories) for 24 hours (or longer with proper dietary adjustments), your body burns stored fat for fuel instead of using muscle glycogen stores as its primary source of energy. When you exercise, your muscles burn stored fat for fuel instead of using muscle glycogen stores as their primary source of energy. Therefore, when you eat less than your daily calorie requirement (calories) for 24 hours, your body burns stored fat for fuel instead of using muscle glycogen stores as its primary source of energy.

Metabolic flexibility is the ability of your body to switch from burning mostly glycogen to burning mostly fat when you’re inactive for a prolonged period of time (i.e. overnight fasting).

When you eat a low-calorie diet and do not do any physical exercise, your body burns more fat instead of carbohydrates (glycogen) for energy. How well your body can adapt to using fat for energy rather than carbohydrates relates to your metabolic flexibility.

Insulin is the primary storage hormone that signals to your body to store excess calories that it doesn’t need right away. It is primarily secreted in response to the carbohydrates that you eat and it promotes the synthesis of glycogen, and then it instructs your fat cells to take up fat from the bloodstream and store it.

Insulin resistance is a condition in which normal amounts of insulin cause a less-than-optimal response. That means that your body requires higher levels of insulin to achieve the same effects (if any at all) and excess glucose stays in the blood where it can cause long-term damage.

Insulin resistance is closely related to metabolic syndrome , which is a combination of medical conditions that put you at risk for heart disease, stroke, and diabetes.

The pancreas secretes more and more insulin to overcome the increased resistance, but it reaches a point where the β cells can’t keep up. At this stage, blood glucose levels rise and this condition is called diabetes.

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Insulin resistance is not the only risk factor for type 2 diabetes. Other risk factors include being overweight, family history, poor diet, lack of physical activity or overeating.

Insulin resistance typically develops over many years and often goes undiagnosed. Although it may not be noticeable at first, the constant strain that insulin resistance places on your β cells will cause them to weaken and reduce in number.

Once your β cells are weakened, your body stops producing enough insulin to keep up with the body’s demand, and you begin displaying symptoms of hyperglycemia (high blood sugar). Without adequate treatment, hyperglycemia can lead to serious health complications like blindness, heart disease, kidney failure, and loss of limbs.

Insulin resistance is the main cause of type 2 diabetes in both adults and children.

Although type 1diabetes is caused by the immune system attacking and destroying insulin-producing beta cells in the pancreas, the main cause of type 2 diabetes is a combination of genetic and environmental factors that lead to insulin resistance.

Although there is no cure for type 2 diabetes, you can manage the condition by eating healthily, exercising and maintaining a healthy weight.

However, even the most energetic lifestyle won’t prevent the long-term complications of uncontrolled diabetes (e.g. blindness, heart disease, kidney failure), so it’s vital to manage your blood glucose levels and take any prescribed medication as directed by your doctor.

As you can see, the relationship between diet and diabetes is very complex.

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It’s not simply a matter of eating a low-carbohydrate diet to manage your insulin levels and blood glucose, because it also depends on other factors like your gut bacteria, health status, and genetic makeup.

What’s the difference between type 1 and type 2 diabetes?

One of the main differences between type 1 and type 2 diabetes is when the condition was first detected.

People who are diagnosed with type 1 diabetes are usually diagnosed within the first few years of their life.

In type 1 diabetes, the immune system destroys beta cells in the pancreas, so the body can’t produce enough insulin to break down carbohydrates and sugars.

With no insulin, high levels of glucose accumulate in the blood, which can cause dehydration, infection, coma and death.

People with type 1 diabetes have to manage their blood glucose levels by taking insulin several times a day, or by replacing their pancreas’ lack of insulin with daily injections of synthetic insulin.

Insulin therapy is effective in managing the disease, but it’s vital that you take the right amount and continue to monitor your blood glucose levels so that you don’t end up with life-threatening complications.

Type 2 diabetes usually develops later in life. The pancreas starts to produce less insulin as you grow older, but it doesn’t completely stop working.

Usually, type 2 diabetes is diagnosed when a person is middle-aged and overweight, although children and adults of any age and at all stages of life are susceptible to developing the disease.

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Although type 2 diabetes used to be known as ‘adult-onset’ diabetes, the number of children developing the condition has risen dramatically over the past few decades.

Although there’s some controversy about why this is, the most likely cause is obesity or being overweight.

Being obese or overweight can affect insulin production and sensitivity, increasing your risk of developing type 2 diabetes.

With type 2 diabetes, your body still produces insulin, but the cells in your body have become ‘insulin resistant’, meaning that they don’t react to the hormone as well as they should.

Insulin resistance is thought to be down to a combination of lifestyle factors (e.g. being overweight, lack of exercise, high levels of cholesterol etc) and genetic factors.

Even though you’re still producing insulin, the amount your body needs to produce increases as you gain weight and the cells in your body become less sensitive to it, so the pancreas has to work harder to produce more insulin to overcome this resistance, which can eventually lead to type 2 diabetes developing.

The good news is that there are plenty of ways to prevent type 2 diabetes, especially if you’re diagnosed with prediabetes.

For people with prediabetes, close monitoring of their blood glucose levels and making changes to their lifestyle can increase their chances of avoiding the disease altogether.

What are the symptoms?

The most common symptom of both type 1 and type 2 diabetes is excessive thirst. You may also notice that you need to urinate more often, particularly at night.

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Other symptoms of type 1 diabetes can include:

Symptoms of type 2 diabetes are more likely to be associated with the long-term complications of the disease, which can take years to develop.

These long-term complications can lead to life-threatening conditions, so it’s vital that you seek treatment and make lifestyle changes to manage your condition as soon as possible.

The long-term complications of type 2 diabetes can include:

How is it diagnosed?

The only way to be sure that you have either type 1 or type 2 diabetes is to visit your GP. They will ask you about your medical history and carry out a physical examination, before possibly carrying out a blood test for GAD Antibodies, and/or an Overnight Glucose Test at a hospital or clinic.

If these tests show signs of you developing diabetes, or you’ve already been diagnosed with the condition, your doctor will also advise you about how to manage your diabetes.

How is it treated?

The main types of treatment for both type 1 and type 2 diabetes are medication and lifestyle changes.

Medication , which is known as ‘insulin therapy’, is only necessary if you have type 1 diabetes. Injections of insulin need to be given directly into the fatty tissue below your skin, but there are different types of insulin with different uses.

Insulin is also available in an inhalable form called ‘Afrezza’, which has to be prescribed specifically for you by your doctor.

Other medication, such as Metformin, may also be prescribed in addition to insulin to help control your blood sugar and stop it from rising too much.

Lifestyle changes involve eating a healthy diet and exercising regularly. If you have type 2 diabetes, your medication may also need to be adjusted in order to manage your blood sugar levels effectively. In some cases, if diet and exercise are not effective enough, you may also need to have a gastric band fitted or have part of your stomach removed by surgery to help reduce the amount of food you eat.

You can manage both types of diabetes without complications by regularly monitoring your blood glucose levels at home and adjusting your medication and diet where necessary.

If you have either type of diabetes, it’s important to seek medical attention immediately if you experience any of the following symptoms:

If you think you may be suffering from diabetes or are worried about your blood sugar levels, speak to your GP as soon as possible.

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Glossary

Antibodies : proteins in the body that Large proteins produced by the immune system to fight off viruses, bacteria and other foreign substances. Some antibodies, called ‘immunoglobulins’, are used to fight off infections. Others affect your blood in different ways.

bind to and destroy disease-causing agents such as viruses or bacteria.

A1C test : a diagnostic test that determines the average amount of glucose in your blood over the preceding three months.

Carbohydrate: a nutrient that, along with fats and proteins, make up the majority of the food you eat. Carbohydrates provide energy for the body, and come in simple and complex forms. Simple carbohydrates include sugars, which are found in foods like fruit, vegetables and milk among others.

Complex carbohydrates include starchy foods such as bread, pasta and rice. Carbohydrates can be measured in grams (g) or milligrams (mg).

Carbohydrate intolerance: a condition where the body has difficulty processing carbohydrates. People with this condition have high levels of blood glucose after eating food containing carbohydrates.

Cholesterol: a fat-like substance present in the bloodstream.

Sources & references used in this article:

Metabolic flexibility and insulin resistance by JE Galgani, C Moro, E Ravussin – … and metabolism, 2008 – journals.physiology.org

Metabolic flexibility in health and disease by BH Goodpaster, LM Sparks – Cell metabolism, 2017 – Elsevier

Skeletal Muscle Mitochondria in Insulin Resistance: Differences in Intermyofibrillar Versus Subsarcolemmal Subpopulations and Relationship to Metabolic Flexibility by P Chomentowski, PM Coen, Z Radikova… – … & Metabolism, 2011 – academic.oup.com

Type 2 diabetes mellitus and skeletal muscle metabolic function by E Phielix, M Mensink – Physiology & behavior, 2008 – Elsevier

Metabolic flexibility in the development of insulin resistance and type 2 diabetes: effects of lifestyle by E Corpeleijn, WHM Saris, EE Blaak – obesity reviews, 2009 – Wiley Online Library

Insulin resistance: metabolic mechanisms and consequences in the heart by ED Abel, KM O’Shea, R Ramasamy – … , thrombosis, and vascular …, 2012 – Am Heart Assoc

Mitochondrial response to nutrient availability and its role in metabolic disease by AW Gao, C Cantó, RH Houtkooper – EMBO molecular medicine, 2014 – embopress.org

Insulin sensitivity and metabolic flexibility following exercise training among different obese insulin-resistant phenotypes by SK Malin, JM Haus, TPJ Solomon… – … and metabolism, 2013 – journals.physiology.org