What Is Metabolism? How Do Anabolism And Catabolism Affect Body Weight?

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Main Category: Nutrition / Diet
Also Included In: Endocrinology
Article Date: 10 Aug 2009 - 0:00 PST

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Metabolism refers to biochemical processes that occur with any living organism - including humans - to maintain life. These biochemical processes allow us to grow, reproduce, repair damage, and respond to our environment. Most people use the term "metabolism" incorrectly for either anabolism or catabolism.

The modern English word "metabolism" comes from the Greek noun metabole, meaning "change", and the Greek verb metaballein, meaning "to change".

According to Medilexicon's medical dictionary, metabolism means "1. The sum of the chemical and physical changes occurring in tissue, consisting of anabolism (those reactions that convert small molecules into large), and catabolism (those reactions that convert large molecules into small), including both endogenous large molecules as well as biodegradation of xenobiotics. 2. Often incorrectly used as a synonym for either anabolism or catabolism."

Anabolism (constructive metabolism) and Catabolism (destructive metabolism)

Anabolism is the building up of things - a succession of chemical reactions that constructs or synthesizes molecules from smaller components, usually requiring energy in the process.

Catabolism is the breaking down of things - a series of degradative chemical reactions that break down complex molecules into smaller units, and in most cases releasing energy in the process.

Anabolism - builds things and consumes energy - making bigger things out of smaller things and using up energy in the process. Anabolism, or biosynthesis, allows the body to grow new cells and maintain all the tissues. The body uses simple molecules to create complex ones. In the same way a builder will use simple building blocks, such as bricks, to create a house. Anabolic reactions in our bodies utilize a few simple chemicals and molecules to manufacture (synthesize) a vast array of finished products. The growth and mineralization of bone and increases in muscle mass are examples of anabolism.

The anabolic process uses monomers to build polymers. A polymer is a large complex molecule made of many small molecules that are similar to each other. Those small molecules are called monomers. For example:

Amino acids, which are simple molecules (monomers)
…through a series of anabolic chemical reactions build…
Proteins, which are large and complex molecules (polymers).

Classic anabolic hormones include

• Growth hormone - a hormone made in the pituitary gland. Growth hormone stimulates the release of the hormone somatomedin by the liver, causing growth.


• IGF1 and other insulin-like growth factors - hormones that simulate the production of protein and sulfate. IGF I and II are involved in the growth of the uterus and placenta, as well as the early growth of the fetus during pregnancy.


• Insulin - a hormone made by the beta cells in the pancreas. It regulates the level of sugar glucose in the blood. Cells cannot utilize glucose without insulin.


• Testosterone - a male hormone produced mainly in the testes. Testosterone causes the development of male sex characteristics, such as a deep voice and a beard. It also strengthens muscles and bone mass.


• Estrogen - a female hormone produced mainly in the ovaries. It is also involved in strengthening bone mass, as well as developing female characteristics such as breasts. It is also involved in the thickening of the inner membrane of the uterus (endometrium) and other aspects of regulating the menstrual cycle.

Catabolism - breaks things down and gives out energy. Using bigger things to make smaller things and releasing energy in the process. Catabolism provides the energy our bodies need for physical activity, from a cellular level right up to whole body movements.

The catabolic chemical reactions in the living cell break down polymers into their constituent monomers. For example:

• Polysaccharides are broken down into monosaccharides
  Complex carbohydrates, such as starch, glycogen, and cellulose are polysaccharides.
  Simple carbohydrates, such as glucose, ribose, and fructose are monosaccharides.


• Nucleic acids are broken down into nucleotides
  Nucleic acids are the chemical basis of life and heredity - they encode our genetic information. They serve as transmitters of genetic information. Examples are RNA (Ribonucleic acid) and DNA (Deoxyribonucleic acid).
  Nucleic acids are broken down to purines, pyrimidines and pentoses, which among other things, are involved in our body's energy supply.


• Proteins are broken down into amino acids
  The amino acids produced by catabolism may be directly recycled, used to make new amino acids, or be converted to other compounds. Sometimes protein is broken down into amino acids to make glucose, which appears in the blood.

When we eat our body breaks down the organic nutrients - this breaking down process releases energy, which is stored inside molecules of adenosine triphosphate (ATP) in the body.

Classic catabolic hormones include:

• Cortisol - known as the "stress hormone", as it is involved in response to stress and anxiety. It is produced by the adrenal cortex, which is part of the adrenal gland. It increases blood pressure and blood sugar, and reduces immune responses.


• Glucagon - a hormone made by the alpha cells in the pancreas. It stimulates the breakdown of glycogen by the liver which causes blood sugar levels to rise. Glycogen is carbohydrate that is stored in the liver and used as a fuel during physical activity. When the hormone glucagon is released it stimulates the liver to the break down glycogen which enters the blood as fuel (sugar).


• Adrenalin - a hormone produced by the medulla of the adrenal gland, adrenalin is also known as epinephrine. Adrenalin causes the heart beat to accelerate, strengthens the force of the heart's contraction, and opens up the bronchioles in the lung. This hormone is part of the "fight-or-flight" reaction animals and humans have in response to fear.


• Cytokines - this hormone is a small protein that has a specific effect on how interactions between cells occur, how they communicate, and how they behave. Examples are interleukins and lymphokines which are released in the generation of an immune response.

The energy stored in ATP is the fuel for anabolic reactions. Catabolism creates the energy that anabolism consumes for synthesizing hormones, enzymes, sugars and other substances for cell growth, reproduction, and tissue repair.

If catabolism is producing more energy than anabolism requires there will be excess energy. The human body stores this excess energy in fat or glycogen. Fat tissue is relatively inactive compared to muscle or organ tissue and other systems in our body. Fat cells, because of their relative inactivity, do not use much energy to maintain themselves, compared to or types of cells.

How is metabolism linked to body weight?

In simple terms, our body weight is a result of catabolism minus anabolism. In other words, the amount of energy we release into our bodies (catabolism) minus the amount of energy our bodies use up (anabolism). The excess energy is stored either as fat or glycogen (stored as carbohydrate mostly in the liver, and also in the muscles).

One gram of fat produces 9 calories (kcal), compared to 4 kcal from protein or carbohydrate.

Although becoming overweight is mostly a result of the body storing energy as fat because there is an excess of it, sometimes hormonal problems or an underlying medical condition may affect metabolism.

It is a common belief that a slim people have a "high metabolism" while overweight/obese people have a "low metabolism". This is very rarely the case. Studies carried out in North America and Western Europe have invariably shown that slow metabolism, or underlying conditions, such as hypothyroidism (underactive thyroid) are very uncommon reasons for most cases of obesity. Quite simply - most overweight people do not have an underlying condition. The weight gain is mainly due to an energy imbalance.

If you are very overweight or obese it may be advisable to have a medical evaluation to determine whether a medical condition is affecting you weight.

There is not much we can do to significantly change our basal metabolism - out metabolic rate when we are resting. Long-term strategies, such as increasing muscle mass, will eventually have an effect. However, determining what your body's energy needs are, and then adapting your lifestyle according to that, will have a much faster effect on your bodyweight.

Our calorie requirements depend on three main factors:

• Body size and composition - a larger body mass requires more calories than a smaller body mass does. People with more muscle in relation to fat will require more calories than people who weigh the same but have less muscle in relation to fat. People with a higher muscle-fat ratio have a higher basal metabolic rate than people with a lower muscle-fat ratio who weigh the same.


• Age - as we get older several factors emerge which result in lower calorie requirement. Our muscle mass drops, resulting in a higher fat-muscle ratio, our metabolism alters slightly, also resulting in a lower calorie requirement. The following age-related factors reduce our calorie requirement:
  
  
  • Hormones - Men produce less testosterone and women less estrogen with age - both hormones are involved in anabolic processes that consume energy. Human growth hormone, which is involved in anabolism begins to diminish as we age. There is definitely a balance away from anabolic hormones, and towards catabolic hormones as we age - resulting in a much higher susceptibility for high fat-muscle-ratio weight gain.
  
  
  • Menopause - As women approach their menopause there is a drop in hormones which make the body use up more energy. Most women find it harder to lose weight at this time. However, experts say menopausal and post-menopausal weight gain is only partly due to hormonal changes. Other aging factors listed here, such as being less physically active and diet may be the main causes in many cases.
  
  
  • Physical activity - Older people tend to be less physically active than when they were younger. This may not just be due to leisure time lifestyle. A large proportion of young people in physically demanding jobs will have sedentary jobs after the age of 45. This may be because of promotion, the way things are done in some sectors, such as the army, police, fire departments, retraining and entering a new field, or early retirement.
  
  
  • Accumulative-waste theory - As we get older there is a buildup of cells of waste products which probably interfere with metabolism.


• Gender - men have a higher basal metabolic rate than women because their muscle-to-fat ratio is higher than women's. This means that an average man will burn more calories than an average woman of the same age and weight.

How can I lose weight?

When you have found out what your daily calorie requirements are, and you are sure you do not have an underlying condition which may be causing your weight gain, you should focus on three crucial factors that contribute to losing weight and maintaining your ideal body weight - these factors also have an impact on metabolism; they are exercise, dietary intake (nutrition), and sleep.

Sleep (too little or too much may have a negative impact)

If you do not sleep enough your neuroendocrine control of appetite can become disturbed, leading to overeating, altered insulin resistance, and a higher risk of developing Diabetes Type 2 - all of which make a person put on weight. Several studies have shown that sleep deprivation damages the body's ability to regulate eating by lowering levels of leptin, the hormone that tells the body when it has had enough.

Scientists involved in the Integrative Cardiac Health Project at Walter Reed Army Medical Center found a consistent link between body mass index (BMI) and length and quality of sleep. "When we analyzed our data by splitting our subjects into 'short sleepers' and 'long sleepers,' we found that short sleepers tended to have a higher BMI, 28.3 kg/m2, compared to long sleepers, who had an average BMI of 24.5. Short sleepers also had lower sleep efficiency, experienced as greater difficulty getting to sleep and staying asleep," said lead investigator Arn Eliasson, M.D.

Researchers from the University of Bristol, England, found that if a child is not getting enough sleep he/she is at higher risk of becoming obese. They believe that lack of sleep may alter hormones so that children end up consuming more food, as well as the wrong types of food.

Studies have also shown that ghrelin levels are higher in people who sleep too little. Ghrelin is a hormone released by the stomach - it tells the brain that you are hungry.

Scientists from Columbia University, New York, found that sleeping too little decreases glucose tolerance and compromises insulin sensitivity by increasing sympathetic nervous system activity, raising evening cortisol levels and decreasing cerebral glucose utilization. This greatly increases the risk of gaining excessive weight, as well as developing Diabetes Type 2. They also found that people who slept too much (nine or more hours) had a higher risk of developing diabetes.

Not only will you risk putting on weight for hormonal reasons caused by sleep deprivation, but you are also less likely to want to exercise. Several studies have found that people who do not sleep enough are less likely to keep up with any exercise program because they are tired.

Try the following measures that may help you get some good, regular sleep:

• Follow a consistent bedtime routine.
• Make the bedtime setting a relaxing one.
• Have a quiet, dark, and slightly cool bedroom.
• Try to get between 7 to 8 hours continuous sleep each night.
• Avoid foods and drinks that contain caffeine.
• Do not have a big meal just before bedtime. But don't go to bed hungry.
• Do not do any vigorous exercise within 4 hours of going to bed (some experts say six hours).
• Get up at the same time every morning.
• Keep to your going to bed and getting up times at weekends, or your non-working days.

Exercise

A six-month trial carried out by researchers from Duke University Medical Center studied the impact of exercise on 53 participants who had led a sedentary lifestyle. The researchers focused on 17 biological facts known to increase cardiovascular risk, including waist size, physical fitness, visceral fat levels, body mass index, cholesterol levels, insulin sensitivity and indicators of metabolic syndrome, a precursor of diabetes type 2.

The trial measured three levels of physical activity: the equivalents of 12 miles of walking per week, 12 miles of jogging per week or 20 miles of jogging per week. Participants worked out on treadmills, elliptical trainers or cycle ergometers in a supervised setting. Not only did they find significant benefits at the end of the trial, but also that exercise intensity was not an important factor.

Lead researcher, Dr. Jennifer Robbins said "When looking at the group as a whole, we found it wasn't the participants with the highest intensity of exercise who accounted for the combined beneficial effects. That should be reassuring for people to know they don't have to do a high-intensity workout to get these benefits of exercise."

Exercise can be divided into three broad categories

• Aerobic exercise
  
  Aerobic exercise has the aim of improving the body's consumption of oxygen. The word aerobic means with oxygen. Aerobic refers to our body's use of oxygen in its metabolic process (catabolic process). Most aerobic exercises are done at moderate levels of intensity for longer periods, compared to other categories of exercise. An aerobic exercise session involves warming up, exercising for at least 20 minutes, and then cooling down. Aerobic exercise involves mainly the large muscle groups.
  
  Running for 20 minutes is an aerobic exercise, while sprinting 200 meters is not. Playing badminton for 30 minutes is an aerobic activity if the movements of the players are fairly continuous. Golf, on the other hand, is not seen as aerobic because the heart rate has not been raised at a sustained level for long enough.


• Anaerobic exercise
  
  The aim of anaerobic exercise is to build power, strength and muscle. The muscles are exercised at high intensity for short durations. A short duration usually means no more than about two minutes.
  
  Anaerobic means without air. Anaerobic exercises improve our muscle strength and our ability to move with quick bursts of speed. When thinking of anaerobic exercise, think of short and fast or short and intensive. Anaerobic exercises include weight lifting, sprinting, intensive and fast skipping, interval training, isometrics, and any other rapid burst of hard exercise.
  
  As oxygen is not used for energy during anaerobic exercise, a by-product - lactic acid - is produced. Lactic acid contributes to muscle fatigue and must be used up during recovery before that muscle can be subjected to another anaerobic session. During the recovery period oxygen is used to give the muscle a "refill" - to replenish the muscle's energy that was used up during the intensive exercise.


• Agility training
  
  Agility training aims to improve a person's ability to speed up and slow down, change directions while maintaining balance and control. In tennis, for example, agility training helps the player maintain control over his/her court positioning through good recovery after each shot. A crucial skill in tennis is to be able to position yourself in the court so that you can hit the ball to maximum effect. Agility does not only help the tennis player get to the ball more effectively and set up for a better shot, it also gives him/her better balance in order to hit the ball.

You should do a combination of two types of exercises

To get the most benefit out of exercise you should do a combination of aerobic and anaerobic exercises. You should exercise five times a week.

Researchers from Heriot-Watt University in Edinburgh, Scotland found that even regular short bursts of intense exercise, such as a short session of four to six 30-second high intensity sprints on an exercise bike every two days, showed a significant effect on the body's ability to metabolize sugars.

Diet

Calorie restriction

Watching the number of calories you consume each day is an important factor in weight control, especially if you want to lose weight.

Severe calorie restriction

However, severe calorie restriction has been shown to be ineffective for long-term success. A severe drop in calories may trigger the body to alter its metabolism so that much less energy is burned, while at the same time storing any energy it can find. Very low calorie diets commonly undermine motivation, often resulting in overeating when the diet is abandoned.

Unless your very low calorie diet is being done with a well qualified dietitian, nutritionist or health care professional, there is a significant risk of malnutrition, which not only is bad for your health, but may also affect metabolism in a way that makes it more difficult to achieve your goal. The USA and UK have the highest proportion of people who go on these types of crash diets - if they worked the USA would not still have the highest obesity rate in the world and the UK the highest in Europe. A much higher percentage of people who are currently obese have been on crash diets compared to people who are currently of normal weight.

A healthy diet

A healthy diet is a well balanced diet. It should include:

• Whole grains - According to the USDA (United States Dept. of Agriculture) we should consume at least 3 ounces of whole grains per day. A whole grain, unlike refined grains, still has the bran and the germ attached. Whole grains are rich in fiber, minerals and vitamins. When grains are refined the bran and germ are removed. Whole grain products include breads, pastas and cereals - they need to be made with 100% whole grain. Whole grain foods and flours include 100% whole wheat, brown rice, bulger, corn, buckwheat, oatmeal (oats), spelt and wild rice.


• Fruit and vegetables - Fruit and vegetables have a high vitamin, mineral and fiber content - these nutrients are vital for your body to function well. Several studies have proven that a good intake of fruit and vegetables may protect from developing heart disease, diabetes type 2, and cancer.
  
  Most health departments throughout the world recommend that we consume five portions of fruit and vegetables each day. This could include either fresh, frozen or canned, or dried fruit and veggies. A portion means either one large fruit, such as an apple, mango, or a banana, or three heaped tablespoons of vegetables. It could also include one glass of 100% fruit or vegetable juice. A fruit/vegetable drink is one portion, no matter how big it is. Beans and pulses can also count as one portion.


• Protein - We need protein for the building and repairing of tissue in our body. Protein-rich foods also include essential minerals, such as iron, magnesium, zinc, as well as B vitamins. The NHS (National Health Service) of the UK says that proteins should make up about 20% of our nutritional intake. Good sources of protein include meat, poultry, fish, eggs, beans, nuts, quorn, soya (includes tofu).
  
  Nutritionists advise that the fat in meat should be trimmed and drained away after cooking. The skin should be removed from poultry. For people who are not vegetarians, nutritionists advise we consume fish at least twice a week, preferably fish rich in omega oils, such as trout, fresh tuna, sardines, mackerel and salmon. The canning process of tuna removes the essential oils, hence only fresh tuna is considered as an oily fish.
  
  It is better for your health to grill, roast or microwave meats and fish, rather than frying them.
  
  Vegans, who do not eat any foods from animal sources, may get their protein from nuts, seeds, soya, beans and quorn. Vegans may have to supplement their zinc and B12 vitamin intake as these foods are not rich in them.


• Calcium (dairy or plant sources) - Dairy products are a good source of calcium which is important for healthy bones and teeth. Dairy products include milk, yoghurts, cheese, and some soya dairy products. Nutritionists say we should aim for low fat dairy products. People who do not consume animal sourced foods can get their calcium intake from broccoli, cabbage and soya milk and yoghurts with added calcium.


• Fats and sugars - Aim for good quality fats, such as olive oil, avocado, or fish oils. Avoid saturated fats, such as those in cream, fried foods and meat. Avoid tans-fat, a synthetically made fat. Avoid adding sugar to your food, as well as sodas with sugar. There are plenty of sugars in the foods we eat.

Written by Christian Nordqvist


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