Why am I asking questions about the evidence-based providence of the Pioppi Diet? It is in part due to my interest in the Mediterranean lifestyle and other diets that have been linked with a healthy long life, but more because I am interested in the use of evidence in informing dietary patterns, as opposed to short term ‘quick fix’ diets that rely on endorsement and anecdote. This is particularly relevant here, as the British Dietetic Association (BDA) chose to include the Pioppi diet as a ‘celeb’ or ‘fad’ diet, and I’ll attempt cover a few of the reasons here.
The first difficulty is the decision to call it a ’21-day’ diet, giving the impression of a quick fix. The book does mention what you should do after the first three weeks, but this is extremely limited so long-term sustainability is left to the individual. The offer of a quick fix was exaggerated further in a piece about the book on the Mail Online website which claimed that seven days of this diet could add 10 years to your life, which is implausible and unsubstantiated. The excuse that this is the journalist, rather than the authors saying it is not adequate, as when this site has misquoted me, I have asked them to amend it and they have.
Secondly, the diet/plan claims it will help you to ‘lose weight, feel great and drastically reduce your risk of type 2 diabetes and heart disease’. This is, at best, theoretical. Three weeks would not be enough to be able to state a significant clinical impact on health. It is hypothetical and plausible but is it evidenced? Well, not yet.
Thirdly, the decision to name the book after the village of Pioppi, Ancel Keys’ home in the Mediterranean, strongly implies a link to the food and habits of that specific place. To understand that it is not a diet specific to Pioppi you need to read the entire book and this critique. Dr Rosemary Stanton has already gone into more detail about why the diet confuses what is meant by the Mediterranean diet.
The most significant question is whether the diet is evidence-based. To consider this, it’s important to appreciate that not all evidence is created equally. Case reports, testimonials and even anecdotes are evidence, but are very low quality and prone to bias without the ability to show causality (perhaps this can even include celebrity or politician endorsements, but they are extremely low in quality). At the other end of the scale are large intervention studies and systematic reviews with meta-analysis, which can, especially if following people up over longer periods of time, show causality.
Much of what the diet recommends is very much in line with existing dietary advice – more fruit and vegetables, more fish, and a lot less sugar. Where it differs is in recommending a very low carbohydrate intake, with very little pasta, bread or rice. The current evidence supporting the role for wholegrain and starchy carbohydrates (but not free sugars) in the diet is significant, and was reported on recently in the UK in the Scientific Advisory Committee on Nutrition’s guidance on Carbohydrates and Health report. It could be argued that reducing carbohydrate may be helpful for the management of prediabetes and type 2 diabetes and is evidence based, which is why my colleagues and I have addressed this in an academic review and in advice available to the public via the BDA. This is not a new evidence-informed recommendation; the Nutrition Working Group for Diabetes UK (of which I am a member) included this as a recommendation back in 2011.
So, what evidence does the Pioppi book look to? The book itself places a lot of emphasis on the PREDIMED study from Spain. This study encouraged limiting red meat and butter to once a day or less. The PREDIMED diet was moderately high in fat (around 40 per cent of energy, slightly higher than the 35 per cent in current UK dietary guidelines) but half of that came from monounsaturated fats from olive oil, nuts, and other vegetable sources, and was low in saturated fat, with reduced butter and red meat intake. This means about the same amount of energy (40 per cent) was derived from carbohydrate.
The diet in PREDIMED was itself based on a diet described in Greece twenty years earlier by researchers who explicitly stated that the Mediterranean Diet was high in complex carbohydrates (such as grains and legumes) and high in fibre (mostly from vegetables and fruits). It has a high ratio of monounsaturated fat to saturated fat.
Perhaps this traditional type of diet might not be suitable for other countries and so the observed diet in the village of Pioppi was adapted to create the chimera that is the ‘Pioppi Diet’? But another study quoted in Malhotra’s book already did that – the Lyon Heart Study. This adapted the principles of PREDIMED to a group of people in Northern France who had suffered a heart attack. Thinking that these people would not take to lots of olive oil, the researchers offered canola (rapeseed) oil and margarine as an alternative to butter. After two years, the rate of second heart attacks in those following the adapted Mediterranean Diet was lower by three quarters.
Perhaps the Pioppi Diet’s addition of coconuts and sweet potatoes to a Mediterranean Diet stripped of bread and pasta was an attempt to adapt the approach to the middle classes and hipsters, but overlooked the need to match it nutritionally?
This brings us nicely to cost and choice. However, perhaps a key attraction of many of the Blue Zones lifestyles and the Greek or Cretan Mediterranean Diet especially was their simplicity and affordability. As pointed out by the authors of the Pioppi Diet, the cost of diabetes is high and rising, but so is the cost of living for many working class families. So, yes the Pioppi Diet will probably work quite well, if you can afford it. After all it is based on eating plenty of vegetables, with lean meat, nuts and olive oil – all mainstays of the evidenced approaches.
However, if you follow what it recommends in terms of tuna steaks and grass fed beef then it certainly will not be cheap. We need to look at a way of finding healthy and good ways to eat which are affordable and acceptable to our communities, especially as those at greatest risk of poor health related to lifestyle are often those with the least money to spend on food. Perhaps we need to consider what an adapted Mediterranean Diet would mean to the UK, after all this is what has been done with the Nordic Diet. We need to find sustainable ways of eating that people can afford, enjoy and achieve.
The Pioppi Diet does a number of things well, despite the short term focus. It looks beyond food to see how our wider lifestyle can affect health. In fact, this is something our group highlighted when studying older people on islands around the Mediterranean. We found that factors such as sleep, mental health and friendship are all associated with a longer healthy life. So, perhaps the idea of ‘dieta’ as a way of life has merits, but that has to have a focus longer than three weeks.
It is time we break free from the dichotomous argument of low carbohydrate vs low fat and move to a food based approach. Dietitians do not use a one size fits all approach and advice is definitely not related to any ‘Big Food’ influence. It is about individuals finding a way that they can eat that they can love and improves their health. This could be lower carbohydrate, lower fat or an adapted Mediterranean Diet – whatever is right for that person. This was neatly summarised by Christopher Snowdon who has previously described it as a bit like the Eatwell guide with added olive oil.
It is hard to say that the Pioppi Diet is truly evidenced, as it combines parts of the evidence which have not been tested together. That does not mean a number of aspects are invalid. However, the suggestion of a rapid and wide ranging effect which does not match the evidence combined with its reliance upon support from high profile individuals justifies the label of a fad or ‘celeb’ diet.
Duane Mellor is a director of the British Dietetic Association, a Senior Lecturer at Coventry University and has consulted with the food industry. But, he remains independent to critique any aspect of nutrition, and as such has also openly challenged the basis of dietary guidelines. He has a PhD in Medicine (Diabetes and Endocrinology) from the University of Hull.