Weight Loss NHS

Why is loosing weight too fast bad for you?

My wife and I decided to go on a diet recently (3 weeks ago) we've completely changed our eating habits and bought exercise machines and weights which we use every night. During the 3 weeks my wife has gone from 17.2 stone to 16.1 and my weight has gone from 22.10 to 20.00 However I have read on many forums that loosing weight too fast is bad for you. Can anyone explain why this is. The only explanation I can find online is you loose muscle however my chest, arm and leg muscles seem to be growing now wasting away. I use the cross trainer every night for 45 minutes and do weights every 2nd night for around 30 minutes. My wife uses the cross trainer every night for 30 minutes and an arobic exercise every night for 30 minutes.

8 Replies

First of all - Well done both of you! That is great progress. I hope you are already feeling the results of your hard work :)

I've also heard that you lose muscle as well as fat if you lose weight too fast. You might end up being lighter but not as fit as you would have been had you lost the weight more slowly. Another reason is that if you eat too little it can be hard to get all the necessary nutrients for a healthy body - calcium, iron, vitamins, etc. If I eat to little I also find I am lacking in energy so my running suffers (slow pace, feel knackered) and I find it harder to focus at work. I lost at a rate of roughly 1lb per week, so it took me about a year to get to a healthy weight. It helped me to remember that it took me several years to put on the weight so I should expect it to take some time to reverse the process!

If you have just started I wouldn't worry too much about losing quickly. There is a tendancy to lose weight quickly at first but it often slows down to a more reasonable pace after that. If you find you lose another stone plus this month, then perhaps have a rethink and add some more calories. As you are doing a lot of exercise then you might need more calories than the NHS 12 week plan suggests.

Good luck!


Thank you for your reply. I will see what the weight difference is over the coming weeks.


Well done for such a complete overhall and for all of your fansastic results so far :) Really puts me to shame!

You may loose muscle mass but if you're eating enough protein every day and weight training then your muscle mass should either stay the same or increase (fortunately protein makes you feel fuller too so it's great for loosing weight). From what I've heard the main reasons not to loose too much weight too quickly is because your weight loss has to be sustainable i.e. any changes made in order to loose weight need to be sustainable over time and not tail off after a few weeks which is why simpler things like walking in a lunch break help people loose weight. It also takes a while for skin to shrink when you're loosing weight so loosing it too quickly can lead to an excess of skin. In addition, psychologically it can be really disheartening to go from large weekly losses to smaller ones after a few weeks/months which in turn can lead to regressing back to old habits.

Having said that, as a general rule the larger the starting weight the quicker the weight comes off. For you having such a complete change in eating and exercise habits the weight loss initially is bound to be quite high so I really wouldn't worry about having larger losses in the first few weeks.

You really are doing amazingly well. Best of luck :)


Thank you for your reply. I will see what the weight difference is over the coming weeks.


Thanks for your reply. I will just see what happens over the coming weeks.


The lower your weight gets the harder it will get to lose it, but I'd say that's pretty good going..do you have a days rest though? your bodies will need recovery time for maximum effect.....one of the real dangers of changing so drastically is keeping up the tough regime...1 of the main reasons why I joined this forum.


Hi dr 1980

Losing weight very quickly leaves you more likely to get gall bladder problems, like gall stones. Very low calorie diets upset the balance between bile salts and cholesterol.

So, slow and steady weight loss is the way to go, but it is quite usual to lose more weight at the beginning of a diet.


Hi dt1980,

Fast weight loss is not good for you - for a number of reasons.

But let's start with what we're talking about. Recommended maximum weight loss is generally 1 kg a week - but that is averaged out. Most people will have ups and downs so that needs to be seen as an average taken over say three or four weeks, not each single week.

(I lost four stone over six months which is at the upper limit of that.)

The main reasons why fast weight loss is bad is that it is usually as a result of people not eating enough to maintain all of their body functions and that usually means they are not just cutting down on fats and carbs but also not failing to take in appropriate overall nutrition in their eating routine. That can lead to dangerous shortages of some nutrients.

I regularly stress that notwithstanding your attempts to reduce your weight, you body must still have the full range of nutrition that it requires to function properly, e.g. vitamins, minerals, ESA's, etc., etc.

Also, your body - which is a very complicated set of systems - needs some time to adapt to weight change and suddenly forcing it to make a very big change can put it under stress. Significant changes in weight alters a range of other things going on in your body.

Now, whilst there are diets such as Very Low Calories Diets, due to the risks involved, these really should only be undertaken under medical supervision.

My advice would be to adjust your calorie intake to get your weight loss to settle down at about 2lb a week on average. It IS common for people to lose weight faster at the beginning of a weight loss regime due to fluid loss, but that usually only lasts a week or two.

If at some point, your weight loss 'stalls' then reduce it down a bit then - again trying to get it (as much as is reasonably practical) to not more than the 2lb to 1kg a week average.

In the final analysis, there sadly are some who excessively restrict their food intake and excessively exercise - in pursuit of the "body beautiful", often in the modelling / film / entertainment industries - who kill themselves by doing that.

Good luck with your weight loss efforts


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