Is weight loss just the difference between ‘calories in’ vs ‘calories out’?

When most people say they want to lose some weight, they normally mean fat loss. But when you look at the maths of fat loss, it seems to be quite a simple thing to do.  Everyone has an energy balance which determines whether they gain weight, lose weight or maintain their weight.

Simply put, the energy balance is the relationship between your energy input (the calories you get from consuming food & drink) and your energy output (the calories you burn up from metabolic activity, breaking down food and any physical activity). The energy balance equation looks like this:

However, different people have different energy needs. These depend on things like their age, gender, how much muscle they have and how physically active they are.  This is why men tend to need more energy than women per day. When it comes to your weight, if you are in a:

• Positive Energy Balance – you consume MORE energy than you burn up = You gain weight
  

• Negative Energy Balance – you consume LESS energy than you burn up = You lose weight
  

• Equal Energy Balance – you consume the SAME amount of energy than you burn up = Weight stays the same
  

So, when you are in a Positive Energy Balance, the excess energy is stored as fat in your fat cells.  As they fill up these cells get bigger, causing you to gain weight and make your clothes feel a bit more ‘snug’ than they used to be. Weight loss is the reverse of this. In a Negative Energy Balance, your body takes the missing energy it needs from your fat stores, making the fat cells smaller, you lose weight and your clothes feel a bit looser.

Simple right?

No, not really!

Research has shown that the ‘calories out bit’ doesn’t work quite as it’s expected to.

What would happen if you added one 60 calorie biscuit to your daily diet.  As a pound of fat has 3,500 calories, this means that you’d put on about a 6lbs of weight a year, every year for the rest of your life.  But this doesn’t happen!

As you gain weight the following happens in your body:

• It has to use more energy to support, repair and replace the new cells and tissue

• You start burning more energy even if you don’t increase your physical activity levels (have a go at wearing a 28lb backpack all day if you want to try it)

As a result of this, the weight gain slows down and after a while starts to level off, even if you’re still eating that extra biscuit.

The bad news is that if you did the opposite and and changed your normal diet and started eating 60 calories less a day, you will lose weight but:

• You’ll burn less calories as your body doesn’t have to use the extra energy to maintain the lost tissue

• The weight loss starts to level off and become less and less

If you go back to your normal diet (as most people do when they’ve lost the weight they want to achieve), you’ll simply start regaining weight again.

A 2010 study in the American Journal of Physiology looked at how weight loss affected peoples muscle efficiency. The study found that:

• Their muscles were around 15% more efficient when they lost weight, mainly due to having less weight to move and ratio changes in enzymes responsible for burning carbohydrate and fat as a fuel.  This meant that it was harder to lose weight as they burning less calories.
• When they gained weight, their muscles became about 25% less efficient so they burnt more calories and pushed them back towards their starting weight.

The same study showed that the biggest changes in the increased muscular efficiency were at low intensity levels (such as normal day to day activities), but not at higher levels (when you’re exercising).

This indicates that exercising at a harder intensity rather than for longer at a lower one, might be a better way for keeping the weight off.

Sources:
– M. Kata & D. Ludwig. Extra calories cause weight gain but how much? JAMA, 2010, 42(1), 65 – 66.
– R. Goldsmith et al. Effects of experimental weight perturbation on skeletal muscle work efficiency, fuel utilisation, and biochemistry in human subjects. American Journal of Physiology, 20101, 298, R79 – R88.