How many of you have heard things such as…

“If you don’t eat enough your body is going to go into starvation mode”

“You’re not losing weight…………you’re not eating enough”

We all know the health implications when it comes to being overweight, but what does eating too little actually do to us?

It goes without saying when it comes to weight loss, we need to be in a calorie deficit (expending more calories than we’re consuming).

To do that we need to be doing a combination of eating less calories and expending more calories through our daily activity and exercise.

Let’s say you do go on a low-calorie diet, chances are you’re going to lose weight very quickly, however more often than not a rebound happens, some of reasons why that happen might become more apparent as you read on.

So, when you eat really low calorie, and lose a lot of weight, doesn’t the metabolism slow down?

Yes, this does happen, but….

Not to the extent you’ll stop losing weight.

Let me explain…

When we lose weight we require less calories to move and carry out our daily activities then we did before, because quite simply there is “less” of us to move around.

If you imagine walking a mile with 10kg in a backpack it’s going to require more calories to walk that mile than if you didn’t have that backpack on your back, this represents what happens to calorie expenditure when you’ve lost weight.

As a result of the metabolism slowing down to accommodate for this, this doesn’t mean you’ll gain weight.

The principle of weight loss hasn’t changed, you’ll only gain weight if you eat more than your new body weight requires and not adjusting your caloric needs to that new lower body weight.

Let’s look at the energy requirements for a 60kg and 70kg fairly sedentary female to maintain their bodyweight:_

70kg - 1850 calories a day / 12,950 a week
60kg - 1584 calories a day / 11,088 a week

If you were 70kg and you lost 10kg of weight and you were still eating for the requirements of a 70kg female, chances are some weight gain is likely to occur, as you haven’t adapting your caloric needs to your new requirements, this new set point is known as adaptive thermogenesis.

As we start losing weight our bodies (which sometimes fight us just to get started) become much more efficient at expending calories as our calorie demands are now less.

As a result, we burn much fewer calories doing the same day-to-day tasks as we did before as our bodies look to conserve calories.

It’s also very common when people lose a large amount of weight that their activity levels, such as their step count, fidgeting, twitching, holding of posture (also known as non-exercise activity thermogenesis - NEAT and non-exercise non-activity thermogenesis NENAT) decreases as a result of the bodies defence mechanism of conserving calories.

That’s why dieting does become much harder once we’ve lost a substantial amount of weight, our bodies are trying to stop us expending calories needed to lose additional weight and it can definitely become frustrating.

The only way forward is to lower your calories further (starve yourself further if you will) and/or increase your activity levels to keep progressing going.

This is where a diet break can be really useful, which involves increasing your daily calories up to maintenance or a little above for a short period of time as a bit of a reload before pushing forward with further weight loss.

The reality is, it is a lot harder once you’ve lost a significant amount of weight to keep that level of progress going due to the reasons I’ve just discussed.

We can't blame our metabolism, it’s just doing its job of efficiently managing our energy expenditure, progress stalls as we don't adapt to it to keep making progress.

One final point on the eating less is just as bad as eating too much, this is a pretty extreme example-

A 32.5 stone (456lbs), 27-year-old male-
- Fasted for 382 days
- Lost 19 stone 10lbs (276lbs) of weight, down to 12 stone 12lbs (180lbs)
- 5 years later he weighed 13 stone, 8lbs (190lbs)

This to my knowledge this has never been repeated or recommended for that matter!

But at that kind of bodyweight it would be fair to say he wasn’t worrying whether he was eating too little or not eating enough, I'm sure he was just happy to have his life back.

It also goes to show, although this was an individual case, the speed of which he lost weight couldn’t have been any faster without surgery, and in a 5-year period only regained 10lbs.

You can read more about it here if you like that kind of thing:

Just to conclude, low calorie diets don't lead to "starvation mode," it isn't really a thing, we won't be lying flat on our backs unable to move because we've just eating a carrot all day.

That's not to say un-necessarily low calorie diets are the way forward either and certainly not for pro-longed periods of time but they do have their place with some individuals.

If weight loss isn't occurring and you start to have thoughts of "am i eating enough?" always remember the rules of weight loss:-

- We need to be in a calorie deficit.

- When you've lost a large amount of weight you need to adjust your daily calorie requirements to the reduction in bodyweight.

- We need to keep our activity levels HIGH as they knowingly or unknowingly reduce as we lose significant amounts of weight, which ultimately decreases energy expenditure and halts progress.