Theory Thursday

Are you a scientist?  A realist? Do you not believe the hype? Do you shiver at the Internet claims of the cabbage soup diet, the egg and grapefruit diet and the meal replacement diets?

picture of a golden egg

Do you long for some real evidence which you find relevant to your health aims?  Well, we’ll try to bring it to you here.  Even if you normally hate science, keep reading.  We’ll also try to translate it into plain English that makes the penny drop.  Then you can understand the best current health science.  Some of it is quite surprising and counter intuitive!  But it works – we know, we tried it.

Basal metabolic rate – BMR

Our bodies are amazing 24 hour machines, they burn calories just doing nothing.  Your basal metabolic rate or BMR is the number of calories you burn per 24 hours if at rest.  What is doing the burning when you’re just resting?  Well, your gut is quietly working pretty hard – extracting nutrients from your food, peristalsing (moving poo downstream).  Your brain is buzzing, repairs are being microscopically carried out all over the place, your eyelids are blinking.  Your bone is remodelling, your muscles are using some energy – amongst a host of other calorie burning functions. 


Modify the burn

You can imagine, then, that a number of things affect the number of calories you burn at rest:

1 – current weight – if there is more of you, there are more cells burning calories hence your BMR will be higher.

2 – current age – the younger you are the higher your BMR.  There are various reasons for this, but one is higher muscle mass.  Peak bone and muscle mass occurs aged 34 so if you’re young and you’re reading this – get building up to your peak now!  If you’re old – don’t despair, you can build some back up again!

3 – sex – men have a higher BMR to women, usually due to their higher percentage of muscle.


Calorie deficit

What does this mean?  Well, in order to lose 1lb of fat per week you need to be in a calorie deficit of 3500kCals, or 500kCals per day.  Very simply, if you have a BMR of 1500kCal and you currently consume 2000kCal a day then a 1500kCal nutrition plan alone might achieve your weight loss aims.  But that isn’t very satisfactory, as you will find if you have tried to do it.  Because as you lose weight (and get older) your BMR will drop and your muscle mass will probably drop and you will end up chasing your tail.  And it is VERY IMPORTANT to stick to no less than 1200kCal/day (unless on a short term very low calorie diet) to avoid malnutrition.

You can’t do anything to stop yourself aging or change your sex (****) but you can modify 3 factors to achieve your weight goal much more healthily and sustainably and create a calorie deficit:

1 – Take in less calories – nutrition plan


2 – Burn more calories – activity plan


3 – build muscle – strength training plan

If you exercise and strength train as well as eating right, not only can you eat more, you will gain muscle.  Although your BMR will drop with weight loss you will find it much easier to maintain.

Lessons learned

I had a very painful lesson to learn about my own BMR.  I had never looked at what it really meant to be so short in terms of my BMR.  I just ate what everyone else ate.  Working out my basal metabolic rate was absolutely sobering.  At 143.2 cm tall I will gain weight if I eat more than 1150 kCal/day (if inactive).  Putting that into context, look at a typically modest English diet:


cup of tea, 2 slices of toast with butter and marmite = 214 kCal,


ploughmans sandwich, pack of crisps, orange juice  = 685 kCal. 


shepherds pie and vegetables, glass of red wine – 528 kCal

total =1427 kCal

(and imagine I might not stop at one glass of wine, I might have pudding, I might have a “snack” – all adding to the calorie count)

As above, if every 3500kCal over your metabolic usage is a pound of weight gained, finally I understood that I would gain 1/2 lb per week and be 133kg (wider than tall!) by the age of 50 if I didn’t do something.  I couldn’t just diet and eat 1150kCal a day – anything less than 1200kCal can lead to malnutrition.  I had to exercise.  Not only that, but I had to build muscle – later on a “theory Thursday” we’ll talk about sarcopenia, but every year past the age of 30 we lose muscle mass (which is metabolically active) and hence our BMR drops and drops every year, so if I didn’t improve my BMR I would be eating less and less each year until I figured my daily caloric intake to avoid weight gain would probably amount to a single peanut!



I like peanuts, but that was not a future I relished. 

“Eat smart, move more, build muscle”

So, now you know why you’ve been getting fatter as you age even though you may not have been eating more.  Be honest and acknowledge the degree to which your sedentary lifestyle is making you lose muscle and raising the risk of weight gain.  Have a look at total lifestyle change – a nutrition and activity plan with strength training that puts you into 500kCal deficit per day (or 3500kCal deficit averaged over a week) until you reach your goal weight:


****artistic licence – in fact you can change your sex

Published by


A tiny hobbit dedicated to saving the world with a decent second breakfast. Also, available to make you feel good in triathlon when you overtake her.......

Leave a Reply

Your email address will not be published. Required fields are marked *