Many a times while talking about body weight, we tend to throw around the term ‘metabolism’.
The friend who eats all he wants and still gains no weight is said to be blessed with high ‘metabolism’.
The sense, in which we use it, is that metabolism is the body’s capability of burning calories.
That is somewhat true but there are a number of factors at play which influence the way our body utilises energy.
Today we are going to cover a number of aspects which will give us a better understanding of what metabolism exactly is and how it regulates our weight.
What is metabolism?
Metabolism is a number of biochemical processes taking place in a living organism.
Metabolism in humans is typically a process where either energy is extracted from the food we consume or the same is used in making up body tissue.
This is particularly defined by two terms:
Anabolism: Small molecules are utilised to make large molecules. Eg: amino acids are used to make proteins
Catabolism: Larger molecules are broke down into smaller ones. Eg: digestion of protein involves breaking it down to amino acids
What is energy balance?
Energy balance is extremely necessary for our survival.
To maintain an ideal balance we say that energy intake must be equal to energy expenditure which translates as weight maintenance. In case of energy imbalance a static equation is used:
Changes in energy stores (Body Weight) = Energy intake- Energy expenditure
However this is not the ideal equation since it does not take into account increasing energy expenditure with increased weight. (Yep the energy we require to sustain ourselves increases with increase in size).
A more ideal equation would be one that is time dependent:
Rate of changes in energy stores (Body Weight) = Rate of Energy intake- Rate of Energy expenditure
So we typically can’t blame than excess energy intake is solely responsible for our weight gain, though it sounds fundamentally correct.
Individuals with low fat oxidation, low energy expenditure, low physical activity will gain weight.
We already have abundant data on energy intake: like what to eat, when to eat and how much to eat. So lets figure out what is energy expenditure.
What is energy expenditure?
Instead of focussing on metabolism or using this term, we should now adapt to altering our energy expenditure which is the rate at which body burns calories.
It comprises of three things:
- Basal Metabolic Rate: It is the number of calories to keep the body functioning.
- Thermic effect of food: It is the calories of energy utilised to ingest and digest food which can be altered by changing dietary composition.
- Physical activity level: It is the most variable component of daily energy expenditure and for a sedentary individual it accounts for 20-30% of the daily energy expenditure.
Note: Body’s capacity to burn calories is more than just metabolic rate. Our daily physical activities and the energy required to breakdown and utilise food also counts.
What is basal and resting metabolic rate?
Basal metabolic rate (BMR) is the energy expended by an individual in standard condition: awake, 10-12 hours of fasting, 8 hour of physical rest, state of mental relaxation and at normal temperature.
Resting metabolic rate (RMR) on the other hand is measured under less restricted conditions.
BMR accounts for energy required to maintain body at normal temperature at rest and a number of processes that are essential for life such as protein synthesis and degradation, RNA,DNA production and repair etc.
For sedentary adults it accounts for 60-70% of the daily energy expenditure.
There is a close relation between BMR and body weight which is why equations are designed to predict BMR from weight.
There are a number of factors that influence BMR:
- Body composition: Individuals with higher lean mass have higher BMR.
- Gender: Men tend to have higher BMR than females.
- Fever: There is a 7% increase in BMR for each degree of rise in temperature in Fahrenheit.
- Stress: Stress raises BMR.
- Smoking or Caffeine consumption: Both of these lead to a higher BMR.
- Hormones: Thyroid hormone influences BMR. Hyperthyroidism raises BMR by 50-70% and hypothyroidism decreases it by 30%.
- Age: Lean body mass decreases with age so BMR decreases. Children have higher BMR than elderly as they are still developing.
- Height: Tall people have higher BMR than shorter counterparts.
- Fasting/Starvation or Undernutrition: These tend to slow down BMR.
- Pregnancy: BMR increases during last trimester.
Myth Busted: Obese or Overweight individuals have a low metabolic rate!
How many times have we despised that thin friend or acquaintance for being blessed with a high metabolic rate or blamed our weight gain on our slow metabolism !
Surprisingly that is so not true.
Here is one study that shows that upper body obesity is associated with increased metabolic rate.
In fact another study shows that overweight men and women have higher metabolic rate than their lean counterparts.
Obese individuals tend to have a reduced metabolism in response to weight loss.
I stumbled upon a research paper which probably has most answers to confounding questions related to metabolism and weight gain. You can find it here.
The authors of this paper suggest that low metabolic rates have been linked with obesity since early papers divided resting energy expenditure with body weight which gave an inaccurate rather low estimate of mass specific metabolism.
Even if you explore different equations for calculating BMR, you will find it is directly proportional to weight.
However this does not defy the idea that low metabolism can lead to weight gain.
It definitely can.
But it would be inappropriate to generalize that every obese or overweight individual suffers from a poor metabolic rate.
Even regular equations can’t predict BMR in obese individuals.
A low BMR can occur as a result of some physical condition or even due to genetic structure.
So how does metabolism predict the possibility of weight gain?
J Galgani and E Ravussin go over the different ways by which metabolism can serve as a risk factor for future weight gain in their paper ‘Energy metabolism, fuel selection and body weight regulation’.
According to them, the following four metabolic parameters are predictors of weight gain:
1. Low metabolic rate
Lower the metabolism, higher is the tendency to put on weight.
This typically does not mean that obese individuals have low metabolic rate.
Several studies have been conducted on Pima Indian population and one of them shows that low metabolic rate despite of being adjusted for factors such as fat free mass and age, proved to be a risk factor for weight gain.
The tendency to gain 10kg weight was 8 times higher in those with low RMR.
2. Low spontaneous activity
Spontaneous physical activity accounts for 8-15% of daily energy expenditure.
It is the physical activity you do daily as a part of your nature and not with the intent to lose weight or resistance training; like simply standing or moving about or even fidgeting. It protects you from fat mass gain.
It varies from individual to individual.
A study reports that Pima Indians express low spontaneous physical activity which serves as a risk factor for weight gain.
Another review study states increasing nonexercise activity can increase daily energy expenditure in a sedentary individual.
3. Low Sympathetic Nervous System activity
Sympathetic nervous system mainly deals with the body’s fight or flight response.
Interestingly activity of this system is found to influence resting metabolic rate.
Individuals predisposed to obesity have low sympathetic nervous system activity compared to equal weight counterparts. It can also result in poor weight loss outcomes of dietary intervention.
4. Low fat oxidation
The kind of nutrients you consume can affect the body’s ability to degrade and utilise it.
For example it can take a week for your body’s fat oxidation capability to match your fat intake, if you have recently started consuming high fat diet.
A study reports that shifting from a low fat to high fat diet can bring about small but steady increases in fat oxidation rates resulting in a positive balance in future.
A research study states that low fat oxidizers have 2.5 times higher risk of gaining weight than high fat oxidizers.
Prior to losing weight, individuals are reported to have low fat oxidation rate and those who are successful at maintaining weight loss have higher fat oxidation rates than those experiencing a weight relapse.
Tips for maintaining a healthy metabolism
If you feel you have a sluggish metabolism or simply want to boost your body’s ability to burn calories here is what you can do:
- Indulge in resistance training.
- Rev up your workout with high intensity interval training.
- Sip on coffee and tea.
- Eat at regular intervals- 6 meals a day.
- Don’t practice crash diets
Metabolism comprises all processes that utilize or derive energy.
Total energy expenditure is the body’s ability to burn energy consumed which is more than just your basal metabolic rate. Overweight individuals actually tend to have a good or better metabolic rate than leaner counterparts.
Genetics, muscle mass and a number of factors affect basal metabolic rate and there are no such remedies that can boost your metabolism to an extent that you will burn fat automatically but even slight elevations are better than nothing.
When incorporated for long term, these tips lead to a healthier lifestyle.