Diet Watch: 5:2 Fast Diet

The 5:2 or Fast Diet originated in the UK by Michael Mosley and has grown in popularity in our diet-oriented culture. 

5:2 Regimen:

Simply put, you are to severely limit your calorie intake 2 days out of the week and eat 'normally' the other 5.  On the "fast" days men should eat no more than 600 calories and women no more than 500. 

Claims:

Weight loss, reduced inflammation, improved insulin sensitivity.

Assessment from a Registered Dietitian Nutritionist:

Practicality Rating: D

The low rating comes from the feasibility of working in 2 days each week to severely restrict your calories while going about your life at work and home.  Think about feeding children normally and trying to "fast", or at work where lunch meetings happen, or on weekends when social events are scheduled.  Maintaining this type of schedule is not practical or conducive to long-term adherence.  Also, this diet is not recommended for anyone under 18, pregnant women, diabetics, people on certain medication regimens (think about taking multiple medications that have to be taken with food), or anyone prone to eating disorders. More on this in the health rating section.

Health Rating: C-

I gave it a C- minus because if you are very careful, you could technically meet all your nutritional requirements with a lot of planning and self-control.  That being said, let me list the problems that arise from following this diet:

• For a lot of people, the severe restriction 2 days a week is going to lead to unhealthy or binge eating on other "normal" days.  Not only does this ruin your healthy relationship with food, but can lead to disordered eating.
• Not for those prone to eating disorders: That can be said for pretty much any diet, since it is the diet mentality that destroys all healthy, long-term, healthy weight maintenance.  But can you see the red-flag here?  Diets appeal particularly to those with eating disorders - and this one could be quite the siren-song for anyone suffering from an eating disorder.  
• Balanced nutrition: When you are having 500 calories a day and enduring the deprivation, think of what you will crave and reach for the following day.  Salad, beans, whole grains and fish?  Most likely not.  Deprivation eating tends to lead to over-eating more empty-calorie foods such as fast foods, cakes, chips etc.  So getting all the calcium, fiber, iron, folate etc. from a few normal eating days a week is not that easy or realistic.  
• Also, since this is not for diabetics, that rules out a huge segment of the population in need of weight management.  
• Even though exercise is recommended on the fasting days, the reality is that it would be more difficult, and less appealing to exercise on those days and so overall activity levels may also decrease.  

Sustainability Rating: D

• Because of the practicality rating, the restrictions on who can participate in this diet, and the health issues, I give the sustainability rating a D.  I have no qualms with an occasional, limited duration, true fast as it definitely does impart some health benefits.  However, a deprivation, pseudo-fast twice weekly is not the long-term solution to our weight-control and disordered-nutrition issues.