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Dangers of the Very Low Calorie Diet

>> Saturday, April 9, 2011

For people struggling with overweight and obesity, there are an overwhelming number and variety of diet strategies that are available in the commercial marketplace.  With the wide diversity of options available, it can be confusing to sort through them, and to know if some are better than others.  One thing is certain: any diet plan that includes a very low calorie diet can be downright dangerous.

A 'Very Low Calorie Diet' is defined as any diet providing less than 800 calories per day.  These diets  aim to supply very little energy, while trying to supply essential nutrients.  They often seem very attractive because of the rapid weight loss that often occurs on these diets.  However, there are several safety concerns with these Very Low Calorie Diets, including the following: 

1.  Potentially fatal heart rhythm disturbances may occur.  These diets cause a rapid shift in water balance, especially in the early phases, which can lead to dangerous alterations in the balance of electrolytes that are important to normal heart function and rhythm (especially potassium).   Over the longer term on these diets, even after the initial fluid shifts settle down, these electrolyte imbalances and heart rhythm disturbances can still occur. 

2.  Very low calorie diets are likely to be nutritionally insufficient.  Because so little food is being taken in, it is very difficult to obtain sufficient amounts of the important vitamins and minerals that are needed for the daily function of our body and cells.

3.  Due to the rapid weight loss that is seen on these diets, there is an increased risk of gallstone formation.  (Any intervention that causes rapid weight loss can cause gallstone formation - weight loss surgery is another example of this.)

In addition to the safety concerns above, the very low calorie diet is highly unlikely to result in successful and sustained weight loss over the long run.  Though they can result in a substantial and rapid weight loss, they teach nothing about how to modify dietary habits in the long term.  Therefore, when an individual stops one of these diets (and they do stop at some point, as they are simply not sustainable over the long term), a rapid weight gain most often ensues, as that person returns to their old habits and way of life. 

In addition, a number of studies have shown that a diet providing 500-600 calories per day does not produce a greater weight loss compared to diets comprising 800 calories per day.  It has been suggested that the body may go in a 'starvation mode' on the very low calorie diets, downregulating its metabolic rate and calorie burn, as an evolutionary tactic designed to survive times of starvation.  In other words, these diets may negatively affect your baseline metabolism while on the diet, such that your calorie burn is lower, thereby leaving you with no greater weight loss benefit, but putting you at all of the risks that come with these low energy diets.

In order to successfully lose weight, the calories in must be less than calories out - no doubt.  However, a permanent lifestyle change that results in a more moderate rate of weight loss is much safer, much more enjoyable, and sustainable!  We generally recommend a weight loss of 1 pound per week, which can be achieved by a typical woman on about 1,200 calories per day, or by a man on about 1,700 calories per day, though this number can vary substantially from person to person.  You can calculate your own caloric requirement for weight maintenance or weight loss using the BMR calculator here.

Dr Sue Pedersen © 2011

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Chris Collins May 14, 2011 at 12:09 AM  

Hi Dr. Sue,

I've been trying to kill the "starvation mode" mania I read from people with whom I'm trying to lose weight.

I've read as many websites, and studies to try to find the root report on the "starvation mode" syndrome.

What I have determined is that starvation mode is an actual bodily process, but it is radically different than what an obese north American thinks about when they consider eating 1200 cals/day.

Famine victims, eating less than 800 calories/day of nutrition-poor food, over some time, will enter a starvation mode.

An obese North American working on portion control, and trying reduce from 2200/day to 1200/day is in now way coming even close to a clinical case of starvation mode. It is one of the dieters popular myths....I believe. How about you?

Dr. Sue Pedersen May 14, 2011 at 7:37 AM  

Hi Chris,

You are correct that 1,200 cal/day does not trigger the 'starvation mode' of metabolism. For a typical sedentary woman, 1,200 cal/day intake will result in a very healthy rate of weight loss of about 1 lb per week. For the typical sendentary man, an intake of about 1,700 cal/day will do the same. You can calculate your own calorie requirements in the right hand column of .

Studies show that diets of less than 800 cal/day do not produce a greater weight loss than those providing 800 cal/day, which is probably because the body's metabolism drops into a lower burning 'starvation mode' as a protective mechanism.

Thanks for the discussion!

Dr Sue

Anonymous July 20, 2012 at 6:24 AM  
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Jacqueline Fisher June 8, 2014 at 9:26 PM  

I know of a woman who eats 1200 cals a day, but exercises 4000 a day. She claims her Dr is more than ok with this. I know that NO Dr would be fine with it as she is -2800 calories a day. This woman has the gall to have a go at me for fasting (and I then eat my TDEE + a little more on the normal days) yet she is doing a dangerous thing & says she knows what she is doing & has lost 3lb. Yeah 3lb of muscle.


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