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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