When we eat, food gets broken down (digested) in the gut. Digested food is absorbed from the gut into the bloodstream, supplying energy and nutrients to the body. The body is made from organs and trillions of tiny, microscopic cells, which work together to keep us alive. Our health relies on this community of organs and cells working together and looking after each other.
As nutrients in the bloodstream reach the cells, chemical reactions take place and molecules are built up, broken down, and used for energy. Chemical reactions happen continuously inside cells, which converts the nutrient from the food we eat into molecules that are useful for the cells. Life needs energy and chemical reactions in the cells extract energy from the food we eat.
The word “metabolism” is used to describe all of these chemical reactions taking place in the cells.
Metabolic health:
The food we digest can be used as fuel for energy immediately, or the fuel can be stored to be used later. As the body is burning, storing, and releasing fuel it has to maintain a state of balance and harmony. This balance is known as homeostasis.
Metabolic health refers to how well the body is able to use and store fuel for energy, while maintaining a state of balance (homeostasis).
The state of our metabolic health can be compared to looking after a car. Good metabolic health can be compared to a well looked after car, which starts first time, runs smoothly, and rarely breaks down. Poor metabolic health is like a car that has been poorly maintained, which struggles to start, does not run smoothly, and breaks down easily.
All parts of the body are involved in metabolic health, but some parts of the body play a key role, including the blood system, gut, liver, muscle, fat tissue, and pancreas.
- Blood system: Blood flows in a network of blood vessels, called arteries, veins, and capillaries. An adult body contains about five liters of blood, which performs many tasks, including the delivery of fuel in the form of sugar (glucose) and fat to all the cells in the body.
- Gut: The gut plays a key role in taking in food and processing it, supplying energy and nutrients to the body.
- Liver: The liver is the main chemical processing unit of the body and responsible for a wide range of functions, including getting rid of harmful substances and converting food into substances that the body needs. For example, the liver can make and store glucose as glycogen, to be released when the body needs fuel for energy.
- Muscle: The muscles throughout the body also include skeletal muscles attached to the bones to help us move. Muscles are a primary site for glucose uptake and storage, while also playing an important part in removing excess sugar from the blood. As muscles process much of the glucose in the body, more muscle mass improves insulin sensitivity.
- Fat tissue: Two main types of fat is stored in fat tissue in the body. Subcutaneous fat is the healthy fat store that sits under the skin and aids metabolic health when subcutaneous fat stores are adequate. Visceral fat sits inside the abdomen, where large amounts increase the size of the belly and waist. This fat is harmful, as it releases chemicals into the bloodstream that increases inflammation in the body, making it harder for the body to stay in balance.
- Pancreas: The pancreas plays an important role in metabolic health, as it releases hormones that help the body to digest, store, release, and use food. The main hormones released by the pancreas are insulin and glucagon, which counterbalance each other to regulate the level of glucose in the blood. Insulin normally keeps blood glucose from rising too high and glucagon keeps blood glucose from dropping too low.
The crucial role of insulin in metabolic health:
The role of the pancreas brings us to the fly in the ointment of metabolic health, namely when insulin no longer prevents blood glucose levels from rising too high.
When insulin is excreted into the bloodstream, it acts like a key in a lock to open the cells in the muscle, fat, and liver, to allow the transport of glucose into the cells, where it acts as fuel to produce energy.
The insulin released by the pancreas increases after a meal, in response to the increase in the levels of glucose in the blood stream.
Glucose comes from the carbohydrates in the food that we eat. Carbohydrates get converted into glucose during the digestive process and absorbed into the bloodstream. When blood glucose levels rise, the pancreas releases insulin into the blood to facilitate the absorption of glucose into cells. In this way insulin lowers blood glucose levels to keep it in the normal range.
Cells may stop responding well to insulin and become resistant to the key and lock effect of insulin and glucose. The inability of cells to respond properly to circulating concentrations of insulin results in a condition called insulin resistance.
The effects of insulin resistance on metabolic health:
The latest research findings indicate that insulin resistance is the main driver of poor metabolic health.
Insulin resistance originates from blood sugar spikes, which are often caused by eating too much food containing carbohydrates, which after digestion enters the bloodstream in the form of glucose. While infrequent spikes are not regarded as a problem, regular spikes in blood sugar levels are problematic.
Daily roller coaster rides in blood sugar levels have detrimental effects on the body. A few examples are:
- High blood sugar levels stimulate high insulin secretion. With such regular spikes, cells become less and less sensitive to the insulin signal.
- Daily spikes in blood sugar levels fuel inflammation in the body. High blood sugar triggers a reaction called glycation whereby glucose is attached to proteins and certain fats. This contributes to increased levels of inflammation.
- The refined carbs that trigger the biggest surge in blood sugar levels are also typically the most fattening.
Blood glucose homeostasis means that normally about one teaspoon of glucose is maintained in the five litres of blood in the body. Whenever large amounts of sugar or starch are eaten, the pancreas must release large amounts of insulin, which try to force the cells to take up glucose from the blood. Cells usually become insulin resistant when they are constantly bombarded by high insulin levels.
Insulin resistance is like having two sides to a coin – on the one side glucose cannot enter some cells as normal and more and more insulin is required for glucose uptake by these cells. On the other side of the coin, high levels of insulin affect many other processes in some cells. For example, high insulin levels drive the body into fat storage mode, as insulin instructs the body not to burn fat, also instructing the liver and fat tissues to turn glucose into fat, and instructing fat stores to hold onto fat, meaning the fat stores get bigger.
Measuring metabolic health:
Unfortunately, there is no single test to determine metabolic health, but there are a few markers for insulin resistance that are commonly used, such as waist circumference (and waist to height ratio), blood glucose levels, blood lipids (fats) in the form of triglycerides and HDL-cholesterol, and blood pressure. The measures vary for different individuals, for example insulin resistance may cause high blood pressure in some but not in all people.
- Waist circumference: This is the distance around the abdomen and measured just above the belly button. This, however, varies by body type, ethnicity, and gender, as a result the waist-to-height ratio (waist circumference divided by height) is a more reliable measurement and should be less than half one’s height. As insulin resistance causes increased fat build-up in the belly and increase waist circumference, a waist circumference that is more than half a person’s height may indicate insulin resistance.
- Blood glucose: Blood glucose levels can only be measured accurately after a period of fasting for 10 hours before the blood test for glucose levels is taken. Fasting glucose should be 5 mmol/L or below.
- Lipids: A fasting blood test for lipids usually gives levels for triglycerides, HDL-cholesterol, LDL-cholesterol, and total cholesterol, but only triglycerides and HDL-cholesterol can give an indication of insulin resistance. Triglycerides are a type of fat which come directly from refined carbohydrates and are mainly stored in liver and fat tissue. Fasting triglyceride levels should be less than 1 mmol/L, which indicates a healthier and less insulin resistant state. HDL-cholesterol (High Density Lipoprotein cholesterol) is a transporter of molecules including cholesterol. A higher HDL-cholesterol level indicates better health, as insulin resistance decreases the amount of HDL-cholesterol in the blood. Fasting HDL-cholesterol levels should ideally be above 1,6 mmol/L.
- Blood pressure: Blood pressure is the measurement of the pressure inside arteries and two measures are taken. Systolic blood pressure coincides with the heart contracting and pumping blood out of the heart, while diastolic blood pressure is the lower reading and coincides with the heart relaxing between beats. Blood pressure for adults should ideally be below 120/80. While insulin resistance may be the most common cause for high blood pressure, many other health factors can also affect blood pressure.
How to Improve metabolic health:
There is no magic bullet or medication to improve metabolic health, as our health is very dependent on lifestyle and behaviors. Four main factors have been identified that can make a significant difference to our current and future health, including improvement of metabolic health.
Nutrition: Nutrition means what, when, and how much we eat and has the greatest impact on metabolic health.
Many foods can worsen metabolic health:
- All types of added sugar in food and drinks, with excessive fructose being particularly bad.
- Ultra-processed foods are typically packaged and boxed with multiple ingredients.
- Refined carbohydrates are starchy processed foods that are rapidly digested, causing sugar spikes.
- Excessive intake of fat can create short-term insulin resistance.
- Regular snacking between meals contributes to sugar spikes.
Certain foods can improve metabolic health:
- Intermittent fasting or restricted time eating within a shorter window of time gives the body time to do cellular maintenance during the fasting period. Also has a profound effect in reducing insulin resistance.
- Real food that has not been heavily processed in a factory and has minimal or a single ingredient.
- The body needs a minimum intake of protein and eating protein also reduces hunger.
- Reducing the total amount of carbohydrates that is eaten can help with insulin resistance. Avoid bags and boxes with barcodes (Dr Ben Bikman 2023)!
- Eat fruit, don’t drink it, as fruit juice may be loaded with fructose.
- An adequate amount of water intake is needed on a daily basis.
Movement: Movement refers to exercise as well as daily general activity. Lack of movement, such as a sedentary lifestyle, leads to a gradual decline in metabolic health. Certain types of movement can aid metabolic health, such as moving regularly, challenging big muscles with resistance exercise, and challenging the cardiorespiratory system with activity that causes an increase in heart rate and breathing rate.
Sleep: The quality and quantity of sleep is important for metabolic health and plays an important role in the control of hormones and blood glucose. The body moves into a relaxed state during sleep and the nervous system switches into repair and recovery mode, while maintenance processes take place in the brain.
Some sleep factors can worsen metabolic health:
- Exposure to a blue light, such as cell phones, computers, or TV before going to sleep.
- Drinking caffeine a few hours before bedtime.
- Eating a large meal before bedtime.
- Alcohol may prevent a restorative and relaxed sleep.
- Intensive exercise before bedtime.
Some sleep factors can improve metabolic health:
- Allow adequate time to sleep, about 7-9 hours.
- Try to go to sleep and wake up about the same time every day.
- Relax before going to bed.
- A routine of going to sleep and waking up in line with the natural night/day cycles.
Mindset: One’s mindset in terms of your way of thinking and how you respond to events affects metabolic health. Chronic stress and focusing on events that you have no control over can worsen metabolic health, while a mindset of being in control of our lives and acting accordingly can lower the risk of experiencing chronic stress.
Conclusion:
Metabolic health plays an important part in the risk of developing metabolic diseases such as heart disease, type 2 diabetes, stroke, liver disease, and kidney disease. Good metabolic health means the absence of metabolic syndrome, which refers to a group of risk factors for metabolic disease, such as high blood pressure, high blood glucose, high levels of Triglycerides in the blood, low levels of HDL cholesterol, and a large waistline.
Interestingly, the old name for “metabolic syndrome” used to be “insulin resistance syndrome”, which highlights once again the fly in the ointment of metabolic health.
References:
Why knowing your BMI is a waste of time. Published 23 October 2023. Blog by Dr David Perlmutter. DavidperlmutterMD. (www.drperlmutter.com)
BMI not a complete measure of metabolic health, research shows. Published 15 June 2023. News Medical Life Sciences. (www.news-medical.net)
BMI alone may not be a sufficient indicator of metabolic health. Published 16 June 2023. Endocrine Society. USA. (www.endocrine.org)
Measuring metabolic health. Published online. Metabolic Health Guide. (www.metabolichealth.guide)
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