The 4:3 diet works on similar principles to 2013's most popular diet - the 5:2 - which uses intermittent fasting. Put simply: you spend five days eating whatever you like and two days consuming a maximum of 500 calories per day.
Eventually, the diet works because the other two days help train you to eat less food.
Dr Krista Varady, the woman whose clinical trials helped to start the 5:2 fasting phenomenon (according to The Times) "has refined the science and devised the Every Other Day diet, aka the 4:3".
This means that you alternate your fast days each week. Varady came across this finding while conducting tests on mice to find out whether diet restriction helped produce anti-cancer chemicals. What she found was that the mice had produced the chemicals but continued to lose weight, and on 'feast' days still hadn't consumed enough calories to outweigh the restriction of their fast days.
Unlike other calorie restriction diets, what she also found during the human tests was that people lost fat, not water. "The 12 women and 4 men in the fasting group had shed between 10lb-30lb and, crucially, this was mostly in fat. There was very little loss of lean body mass (lose muscle during dieting and you’ll burn fewer calories after dieting and regain your weight – as fat)."
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How To Lose Weight Healthily
Does it sound too good to be true? Nutritionist Emily Maguire says that you need to be savvy about what you eat on your feast days.
"Intermittent fasting has been around for a long time and the people who have been practising it (such as Brad Pilon), would ensure that the days you are eating, it is with proper nutrition. If you simply eat a lot of high sugary and processed foods on your non fast days, you will lose all of the benefits you are trying to achieve."
Fasting for two days requires such a reduction in calories that it might be hard for people to stick to it for an extra day, and it will be a challenge to stick to 500 calories and get all the necessary vitamins for your body.
Dr Frankie Phillips from the British Dietetic Association (BDA) says: "To achieve such a low level of calories you would be able to consume only calorie-free drinks such as black tea or coffee or water. Foodwise, it might consist of a couple of scrambled eggs for lunch and a small piece of poached or grilled white fish with vegetables. The 4:3 diet also recommends that breakfast is omitted."
Having been told repeatedly that breakfast is essential for kickstarting your metabolism, this may involve a whole new approach to how you eat.
"Practically speaking," Dr Phillips adds, "the 4:3 diet is likely to be more difficult to follow. With such a severely restricted diet for effectively 50% of the time, it’s more difficult to consume all of the vital vitamins, minerals and essential omega-3 fats that the body needs for health and functional maintenance."
Alice Mackintosh, nutritionist at The Food Doctor says that while there are obvious benefits judging by evidence "particularly in terms of the reductions in chemical markers that appear to increase risks of heart disease, cancer and Alzheimer’s," she adds: "Let’s not be misled by this though, because the prime reason people embark on a diet is for weight loss."
Her key concern, which is similar to other health experts is that the diet encourages calorie counting, which isn't a sustainable path to eating healthier or understanding food better.
"Given that the diet involves eating pretty much whatever you want on the non-fasting days, it doesn’t reinforce the good eating habits that normally prevent us from gaining weight in the first place," she says. "The upshot? Putting weight back on when you got back to eating normally.
"The fact that the diet doesn’t urge those that partake to think about what they are actually putting in their mouths holds another shortfall. As long as it fits into the calorie quota, people can eat what they want and still lose weight. Ultimately this isn’t conducive with good health and doesn’t put ownership on to the dieter to take responsibility for their health."
Apart from omitting breakfast on fast days, the other key difference with the 4:3 is that you have to weigh yourself every day.
Dietitian Priya Tew acknowledges that there are 'good principles' but says: "I would disagree with weighing yourself daily, this can get confusing as your weight changes over a day and a week and is not just influences by what you eat. Instead I would recommend weighing weekly, at the same time and the same day each week."
NUTRITIONIST NAOMI MEAD'S SUGGESTION OF WHAT TO EAT ON FAST DAYS
My advice to those following the 4-3 diet, would be to plan your "fast" days well, to ensure you are getting a good balanced diet.
Vegetables such as broccoli and cauliflower are fantastic because they are bulky, but are low in calories, so you can eat a good sized portion. You also need to ensure that you are getting a good source of protein in the form of lean meat, fish, eggs, tofu or beans/ pulses. Stick to a whole-food diet, and avoid processed foods.
An example menu may be:
Lunch: Spicy lentil & tomato soup, 1 clementine
Dinner: Salmon steak, 2 level tbsp brown rice, half a plate steamed green vegetables.
Snack: Miso soup and handful of grapes
Lots of fluids (water & herbal teas) sipped slowly and regularly throughout the day.
Weight loss expert Steve Miller has a much stronger opinion of the diet.
He says: "I would advise people to avoid fasting and instead simply follow an 80-20 rule, eating well 80% of the time and a bit of what you fancy 20% of the time. For me that is much more sustainable."
Francesca Fox, heath expert and writer of Francesca's Fit Kitchen says: "A great guideline for diets in my opinion is this - "would you give it to a child". I think most would not choose to starve their children for random days at a time. So I beg the question, as adults why on earth do we feel the need to do just that?"
Our verdict is that the 4:3 might be good for weight loss, but not for sustainable healthy eating. Although Varady says that you can up your intake to 1,000 calories on fast days once you've reached your goal weight.
Chloe Phillips, HuffPost UK blogger and dietitian says: "We need to value the importance of nutritional adequacy for health rather than simply cutting calories for weight loss, and I suspect it would be very difficult to meet 100% of your micro-nutrient requirements when fasting 182 days of the year. Let's not cut corners - what ever happened to balanced eating?"