A common question I am asked is about rapid weight loss associated with very low calorie intake.
Recently I have been increasingly asked about the 700 calorie a day diet which was used in part during a recent BBC documentary. This is termed a very low calorie diet by nutritionists.
At that level, losing weight wouldn’t be your main concern long term as it’s highly likely you’d develop some health problems. However that’s not to say that very low calorie diets don’t have their use.
There was a documented study on an obese male who lost 125kg (originally 207kg) by literally eating nothing for a year.
Mr AB was monitored by a doctor and a team of scientists all the way through and given vitamin supplements and most notable potassium so as to prevent cardiac issues.
So 700 calories a day may not be life threatening as such but it’s most likely going to be hard to sustain that for a long period.
In my experience working with clients who have tried to do these extreme calorie restriction diets. Most end up sticking to it for a while. Then a life event or some other stressor comes along that breaks their will power.
This type of diet will be highly likely to make you feel tired and moody. Lethargy during the day will be higher as the body will create an element of adaption. This doesn’t slow down your metabolism as such but stops you being as active.
This is known as NEAT restriction. Non Exercise Activity Thermogenesis.
It’s the energy you burn while not exercising and you’ll find that when you are in a calorie deficit for a long period you will become more lazy.
- Sitting watching a programme you hate on the TV as the remote is across the room and you can’t be bothered to get up.
- Waiting till the last possible moment to get up to walk to the toilet.
- Driving for 20 minutes around the car park to find the space 1 metre closer to the shop door instead of the many empty ones 2 minutes walk away.
Metabolic shut down is kind of a fallacy
Even looking at very low calorie studies. Basal metabolic rate didn’t slow down to a great extent. You still need a certain amount of energy to maintain body function so the body tries to restrict you on anything else.
This is not metabolic shut down or slow down, you are running at the same metabolic rate (within a certain margin) the body just stops you doing anything extra.
This is reducing your EER – Energy Expenditure Rate in the day.
In Laymans – the total energy you burn from doing stuff.
If you do less stuff you burn less.
Think of it in terms of fuel in a car – you need a certain amount to keep the engine running. The miles you do determine how much you use and how quickly you use it. If you drive faster you burn through fuel quicker, if you keep your revs and speed down you can drive more economically.
700 calories a day is not generally advised as it’s unsustainable for most people.
You’re highly likely to break. Then end up stuffing your face with a ton of high calorie food. The result is the deficit you created eating 700 calories is quickly neutralised.
If you are going to do very low calorie dieting then taking a multivitamin supplement is highly advised. It’s also advisable that you eat at least 1g/kg bodyweight of protein in order to help maintain muscle.
As to how much you will lose – that depends on your deficit.
There are calculators on the web to work out your BMR (the level of energy you need to exist) and your EER (the energy you burn in the day)
To work out how much weight you would lose
- Work out your EER
- Minus 700 calories
- The remaining amount multiply by 7 to get a weeks worth
- divide by 7700 to get the amount of kg of bodyfat you may lose.
(a 7700 calorie deficit will use approx 1kg bodyfat)
So for a 100kg male with an EER of 2500 calories
- 2500 – 700 = 1800 (these are the calories your body needs to use from stores to keep you going)
- 1800 x 7 = 12,600 calories your body would need to find from stores in the week
- 12,600/7,700 = 1.64kg of fat that could be lost per week. IF it all comes from fat.
In reality it will be more than this as you will use up your muscle glycogen stores as well as body fat and at 700 calories you won’t replace them to a great extent.
So for every gram of glycogen you use you’ll lose up to 3g of water as well.
Also potentially at that low level you will eat into muscle protein stores a little bit after a while.
So our 100kg male may actually be looking at 3kg a week. Even more in the first few weeks as glycogen and water drops rapidly.
All this is, of course, speculation and will depend on your own variables.
Personally I wouldn’t advise this for long.
Maybe a week or two with a return to a higher calorie level but still within a deficit amount which is easier to manage.
As a nutritionist I have done low calorie kick starts with clients who are super motivated in order to get some weight off fast. However this is not an approach I would use with everyone. I would also not do it for longer than a few weeks.
If you need some further help with planning a more realistic diet then you can download my diet blueprint.
If you would like all the hard work done for you. My Target Lean body program helps you to pick foods you like to eat in the right quantities and keeps you on track with motivation and daily coaching.