Could this be the most useful fasting system?

With increased focus on obesity during the pandemic, fasting certainly looks like remaining a very popular trend in dietary health and general wellbeing, with over 10,000 results showing up for intermittent fasting books on Amazon alone.

There are lot of claims for fasting, from the relatively modest (quicker weight loss) to the potentially life changing (greater protection against cancer, or faster recovery if you are undergoing treatment). With a big serving of money to be made from book sales and media appearances, you have to be very careful which system you go for.

One fasting diet which seems to be getting a lot of support from respected sources is the 2 Day Diet, jointly developed by Dr Michelle Harvie, an award-winning research dietitian from Manchester University Hospital who is also funded by Prevent Breast Cancer. She’s published a popular book on the 2 Day Diet and as its strapline says, the diet involves dieting for two days a week and then eating the mediterranean way for five.We caught up with Dr Harvie to find out more.

There are lot of diets out there involving regular fasting days. What is so special about your 2-Day Diet, and how does it differ from the other popular programmes, such as those promoted by Dr Michael Mosley

I developed it with Professor Tony Howell in 2006 and since then it has been been tested with over 600 people in our research studies. These have shown it is relatively easy for people to follow and highly effective for helping people to lose weight. The diet includes two (ideally consecutive) days where you eat low carbohydrates and low calories, and include healthy protein foods – fish, lean meat, eggs fruit and vegetables – along with low-fat dairy and a few healthy fats. We recommend a healthy mediterranean diet on the other five days of the week – you can find out more about good recipies or meal ideas online.

The fast diet promoted by Michael Mosley, and other intermittent diets based on it, were inspired by our two-day diet research. They typically recommend 600 kcal on two days per week, often of any foods, and no guidance for the other days. These diets became popular in 2013 before they had been researched. Our 2 Day Diet however, was the first researched and evidence-based version. The diet is based on sound principles to meet nutritional requirements and is designed to promote satiety, or a feeling of fullness – therefore making it easier for people to follow.

Put simply, how can your 2-Day Diet boost people's health and energy levels?

The diet was designed to help people who are overweight/ obese to lose weight. We find that 60% of people who start the diet manage to successfully follow it and mange to lose more than % of their weight. This in turn will reduce their risk of cancers and other major illnesses: breast cancer by 25%, diabetes by 60%, and heart disease and stroke by 30%. As you would expect, people feel more positive and have more energy when they lose weight. Many people report feeling really good, and energised on their restricted days

Is it suitable for everyone? Are there any downsides?

There may be a problem for older frail people as they need to eat regular protein to maintain their muscle mass. It also not recommended for children or adolescents. However, a recent Australian study tested intermittent diets for teenagers with obesity, which involved three low-calorie days a week alternated with normal eating days. It showed that intermittent diets which were part of a supported programme were ok. The teenagers were able to follow the diet and lost weight, with improvements in well being. There was also no obvious indication it was causing eating disorders. However, the studies did not look at growth, or longer term effects. Diets during teenage years need to deliver enough energy and protein for growth, and enough iron and calcium. It’s important that teens have the right diet to ensure good concentration and learning.

You do amazing research on breast cancer prevention. What, in summary, are the latest findings about the benefits of intermittent fasting and cancer prevention/recovery?

We have tested the diets in women undergoing chemotherapy for breast cancer and presented the results at conferences – these show that these women can follow the diet. The diet may help prevent gains in weight with chemotherapy, reducing the severe side effects with some (but not all) treatments. We are currently testing if the 2 Day Diet can help improve the effectiveness of chemotherapy for women with metastatic breast cancer and you can find out more here.

Do you think governments should be doing more to push diets with intermittent fasting like yours – could it help with the obesity epidemic?

A lot of people are choosing to follow these diets by themselves with often good effect. We have been working with dietitians and the teams within the National Health Service to allow them to use our diet resources so patients can be offered these diets when referred for weight loss. The evidence of the benefits is certainly accumulating, and the 2-Day Diet is a viable alternative weight loss diet for people who are overweight/obese. What’s more, you can easily return to it if you wish to lose any weight you may have regained.

There are lots of different fasting diets. How do you know which ones are best for you?

The NHS will recommend the ones which show good research and an evidence base, are nutritionally adequate, and are backed by long term data. Our diet, for example, has been recommended by the British Dietetic Association. We need a range of approaches for healthy diets to cater for different preferences and eating styles, and also different health issues. Some people will do better with standard daily dieting than intermittent diets, so the latter are another useful tool in the tool box to use.