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From the Atkins diet, through Paleo and now Keto, low-carb high-fat (LCHF) diets have been all the rage in the world of weight-loss and health for the last couple of decades. These have been producing great results despite contradicting many government guidelines on healthy eating that still focus on reduced fat and an energy intake dependant on about half carbohydrates. More recently, there’s been a lot of publicity around reducing sugar (a simple carbohydrate) consumption to support good health, and even using LCHF diets to put type 2 diabetes into remission, so I was quite surprised to last week suddenly read the headline “Low carb diets could shorten life”, as this seems to go against the trend of the increasing scientific literature.
The headline is based on a new paper published in The Lancet Public Health. In order to qualify as a Registered Nutritional Therapist, I had to undertake extensive training in reading and interpreting research papers, understanding the statistics and assessing the reliability of data presented, so I was keen to take a look at this myself. What I found is definitely food for thought, and certainly not the headline picture being painted by the media… I’ve tried to summarise here a couple of key points I took away from my reading, and hope that they will be useful for you too when deciding how to structure your diet to a long and healthy life.
First of all, the 25-year study, which infers a LDHF diet will reduce longevity, was based on surveying people on what they ate at 6 points in time from 1987-2017. However, the results are extracted from the dietary information obtained from only two of those surveys (taken between 1987-89 and 1993-95). The question I therefore ask is “why not use the more recent data too?” So much can change over the course of 25 years, I want to know these people are really still eating the exact same foods they did in 1987 before I make a judgement on the extent of its effect on their lifespan.
I was also concerned by this statement: “Participants who consumed a relatively low percentage of total energy from carbohydrates [ie the LCHF participants]… were more likely to be young, male, a race other than black, college graduates, have high BMI, exercise less during leisure time, have high household income, smoke cigarettes, and have diabetes.” Could the fact that they were non-exercising smokers have also played a role in their reduced life expectancy? Adjustments in the statistical analysis were made for these factors, but to me this invokes the old statistical example: “shark attacks increase in-line with ice cream sales”, and I proceed with my assessment with an increased sense of scepticism.
Secondly, the paper is not based on just one study, but is instead what is referred to as a “meta-analysis” – that means that the results are a cumulation of multiple other studies too. Whilst this type of study can be valuable for gaining a good understanding of data over a larger sized sample, it doesn’t necessarily mean that all the data is completely comparable. In this instance, the result is broad classifications of complex food groups being “mashed” together for a complete picture, rather than accurately and specifically giving useable data on clearly defined specific food groups for increasing longevity and health.
There is little differentiation, for example, between different types of carbohydrate. One thing I tell my clients and teach in my EAT TO THRIVE classes, is that all carbohydrates are not equal – we know that the glycaemic index (GI) of a food plays a huge role in its metabolism and therefore the effect it has on our health. Simple sugars act very differently to complex wholegrains, yet both are categorised as “carbohydrates”. There is also a huge difference in nutritional profile between eg. a salad and a pizza – both largely carbohydrates, one packed with fibre, vitamins, minerals and phytonutrients, the other? Not. This is also true of other types of fats and proteins – outside of the headline, some attention was paid to animal versus plant sources of these, however this is still a simplified classification of a much more complicated group of nutrients (processed meats versus organic free-range chicken or fish, for example) for which there is much more comprehensive data available.
So, based on this study, how likely am I to recommend to my clients that they should switch away from a lower carbohydrate diet in order to lead a long and healthy life? I hope you will have deduced by now – not likely at all. For now, I will continue to advise a balanced diet of vegetables, wholegrains, good quality fats and proteins which follows an educated interpretation of “low carb” informed by multiple other robust scientific studies. And as for this headline? Whilst the occasional indulgence in “bad carbs” will probably not shave too many years off your life, it’s most definitely not conclusive evidence to support the “absolutely everything in moderation” mantra and over-indulge in them on a daily basis. Whatever you prefer to eat, remember to take these headlines with a pinch of salt, and learn how to really EAT TO THRIVE.