I'm going to get straight to the point.
There is not much we can do to have a lasting and significant effect on our metabolism....sorry.
Keep reading though, because I'm going to go through and explain the common misconceptions around metabolism 'boosts'.
When we are still, there is a minimum number of calories needed to keep all essential chemical reactions going and organs functioning to ensure that we stay alive. These include breathing, heart rate, brain activity, kidney function, liver function and cell growth and repair. This is called our basal metabolic rate (BMR), and accounts for around 80% of your total energy requirements. We have minimal control in changing this, instead it is largely influenced by age, body composition, gender, genes and disease.
What does it mean to have a 'fast' or 'slow' metabolism?
A slow metabolism will likely mean a slow basal metabolic rate (BMR) and there can be many reasons for this. A slow metabolism can be the symptom of a medical condition such as hypothyroidism (an under-active thyroid) or Cushing’s syndrome (where there are high levels of a hormone called cortisol in the body). Both can be diagnosed and treated under the NHS. Metabolism can also reduce with age as the body gets slower at growth and repair and as physical activity reduces.
Symptoms of a slow metabolism include: tiredness, weight gain and muscle aches
It is common for people to self-diagnose themselves as having a slow metabolism because they are experiencing unwanted weight gain or difficulty in losing weight. The UK’s National Institute for Health & Care Excellence (NICE) estimate around 2% of the UK population has been diagnosis with hypothyroidism so it is quite a rare condition to have (NICE guideline [NG145]).
Fast metabolism will mean the opposite of having a slow metabolism. Chemical reactions occurring in the body are taking place more rapidly than it would normally do for the average person. Symptoms of a high metabolism include unintentional weight loss, sweating and an irregular heart rate.
Now, let's debunk some myths
1. Eating certain foods can boost your metabolism
Claims that green tea, black pepper, cayenne pepper, coffee and energy drinks speed up metabolism are typically backed by weak evidence. Any increase in metabolism has been shown to be marginal and short lived.
2. Eating small meals during the day increases your metabolism.
Again, there isn’t any strong evidence that shows that eating little throughout the day boosts the speed of your metabolism.
3. Exercise boosts your metabolism long after you stop.
Your metabolism will increase during exercise and will remain high for about an hour after you finish exercising but it will go back to its baseline rate after that. It’s important not to overeat on calories pre-work work out in the hope that your post exercise metabolic rate will burn off all those additional calories.
4. Why does our metabolism slow as we get older?
Metabolism can seem to slow down with age because we tend to become less active as we get older. Less activity along with slower growth and repair systems as we get older and can mean that the metabolic rate can lower. People often find that their appetite reduced with age. Eating less means that there is less food break down processes and chemical reactions for the body to work through.
5. Top foods to boost metabolism?
Sadly, there aren’t any quality studies that have shown a single food item to produce a significant and long-lasting effect on metabolic rate.
People who struggle to lose weight often blame a ‘slow metabolism’ without looking at other things that could be at play. Research shows that we often under report what we eat so it is more likely that we are eating more calories than we need instead of an low metabolism.
So what can you do ?
Eating small and frequent meals throughout the day is however a good idea as it means that you are less likely to feel hungry and less likely to draw for calorific snacks or drinks.
I would suggest focussing on increasing and maintain a good level of physical activity, preferably a combination of aerobic (the kind of exercise that gets your heart racing and breathing heavier) and weight bearing exercises.
Aerobic exercise is an effective way to burn calories. We should aim for about 2 ½ hrs a week and this can be walking, climbing stairs, cycling or swimming. Splitting this into 5 x 30min sessions or incorporating aerobic exercises into your day is a great way to split it across the week.
Weight bearing exercises help to build muscle. Muscle is metabolically active (it requires energy to function) whereas fat stores are largely metabolically inactive. Muscle burns more calories than fat, so increasing your muscle mass will help you lose weight. We should aim for 2 or more days a week of weight bearing exercises that engage all major muscle groups (legs, hips, back, abdomen, chest, shoulders and arms).
To promote weight loss, maintaining regular physical activity along with addressing eating habits will be more effective than trying to increase your metabolic rate through food swaps.
Thyroid disease: assessment and management. NICE guideline [NG145]
Cowley MA, Brown WA, Considine RV. Obesity: the problem and its management. In: Jameson JL, De Groot LJ, de Kretser DM, et al, eds. Endocrinology: Adult and Pediatric. 7th ed. Philadelphia, PA: Elsevier Saunders; 2016:chap 26.
Hodgson AB, Randell RK, Jeukendrup AE. The effect of green tea extract on fat oxidation at rest and during exercise: evidence of efficacy and proposed mechanisms. Adv Nutrl. 2013;4(2):129-140. PMID: 23493529 www.ncbi.nlm.nih.gov/pubmed/23493529.