As those of you that read the Weekly Wellbeing Round Up will be aware, there was a bit of a scuffle last week in the media about the low carbohydrate diet. This all kicked off due to the publication in the Lancet Public Health of a prospective cohort study and meta-analysis which suggested there might be an association with lower carbohydrate diets and increased mortality. This gave rise to sensationalist headlines in the press, linking low carb diets to a grim, early death. The low carb vs low fat battlelines were already drawn up and ready to go of course, so volleys of invective were being fired each way sooner than you could type twitterspat. It was a particularly unedifying spectacle to outside observers, to whom it may have appeared that the anti-low carb lobby were crowing triumphantlythat this was the nail in the coffin whilst the low-carbers circled the wagons and sat with their fingers in their ears.
So in this week’s post I am attempting to make sense of the evidence, pointing out a few obvious things and making practical recommendations about the place of low carb diets.
I will start with a disclaimer: I am currently eating a low-ish carb diet. I mentioned this in a previous post about my real life wellbeing week. I have lost about half a stone in weight having never managed to lose any in the past by just cutting back on the calories. I’m not a fanatic. I have friends and family who have found this approach similarly helpful. I haven’t written a book on low carb, I don’t run a expensive private clinic or have any merchandise to sell. I will occasionally raid the biscuit tin in reception when I am peckish. I still enjoy a beer and some nibbles with my colleagues in the pub on a friday. It’s one of the best parts of my working week. If the price I pay for this is indeed a grim and premature death, then I consider that an acceptable trade-off.
The Evidence
The problem with the evidence is that there’s both a lot of it and not enough of it. Plenty of cohort studies asking people what they think they ate 25 years ago. Not so many randomised controlled trials comparing low carb to very low carb to moderate carb to low fat etc, with long term outcomes that affect people’s lives (e.g. heart attack, stroke etc). In fact for not so many, read none at all. Plenty of data around effects on blood sugar, cholesterol and blood pressure, but not the really important outcomes. There are lots of meta-analyses looking at the same subject which have come to quite different conclusions. This is due either to the variable quality of the studies that were included or how the analysis was done. The latter in turn may be affected by where the person or persons conducting the meta-analysis stood on the issue. It is widely agreed that more good quality long term data is needed.
The negative
It’s important that advocates of a low carb diet be honest about the lack of clinically significant long term outcomes from properly conducted studies (i.e. randomised controlled prospective studies). Anyone that can tell you their low carb diet plan has been proved to result in fewer heart attacks and strokes is at best wildly optimistic and not understanding of what constitutes proper evidence, confused by the difference between causation and association , or just lying. Quite a few meta analyses have found that the low carb diet is not superior to the low fat diet. Fair enough. Let’s think about that though…”not superior to”. Which may also mean “just as good as”. As in these position statements from Diabetes UK and the NHS UK website. Drug companies make new drugs that are better than placebo and equivalent to many existing products and they get licensed, accepted and used widely..so why do we have to prove the low carb diet is better than anything else to consider using it?
To be clear, there is no credible evidence that low carb diets cause harm. Anyone intellectually lazy enough to have read the Lancet publication and newspaper headlines and said “well, that’s that then” deserves a intellectual kick up the backside. The study is worth discussing but it simply cannot hold all the weight that some seem to be requiring of it and it does not prove causation. A drug would not be licensed if it couldn’t be proved it caused a positive outcome and neither would it be withdrawn unless it could be proved it caused negative outcomes (and sometimes not even then…that’s another topic!). Here is a link to Dr Zoe Harcombe’s excellent detailed analysis of the study.
The positive
Whilst there are meta-analyses that can be drawn upon by both sides it seems clear to me that that there is reasonable evidence from both meta-analyses and individual studies that the low carb diet is at least equivalent to the low fat diet in effectiveness and may even be slightly better in specific patient groups. That’s as strongly as I’m putting it. Proponents of the low carb diet should not claim it is a magic bullet, and sceptics should not dismiss it purely because it isn’t one. The areas where there is, in my view, sufficient evidence to consider it as part of the dietary tools available to us are diabetes (including possibly gestational diabetes), pre-diabetes and obesity. Relevant links below if you would like to do some further reading.
Diabetes
Improved HbA1c, triglycerides and HDL in Type 2 Diabetes
Best dietary approach for reducing HbA1c in Type 2 Diabetics
Obesity
PLOS One meta-analysis of LCD vs LFD in obese or overweight patients
LCD’s result in decreased fat mass, if not a greater long term weight loss than LFD’s.
Reflections
Everyone has either a starting position, personal experience, bias or vested interest in this area. We should acknowledge this. For most people, a low carb diet inevitably involves calorie restriction, which will clearly contribute to weight loss. Low carb diet advocates should acknowledge this. There are a variety of dietary options that are available to us and some will work better than others for each individual…so health professionals and individuals need to explore what is likely to be the best option in each individual and their situation e.g. I would not recommend low carb high fat diet in someone with Familial Hypercholesterolaemia (an inherited condition causing very high cholesterol). Neither would I recommend a moderate to high carb intake in someone with diabetes. We need the right tools for each situation.
We are not coming from a healthy, normal baseline in developed western societies such as UK and US…we massively over-do beige carbs and our rising obesity and overweight figures bear witness to this. It feels intrinsically right to me that we aim to reduce the portion of our diets that has very little if any nutritional value and is clearly contributing significantly to the rise in obesity and related conditions. Evidence changes all the time. When I was a junior doctor, I would have failed my exams for membership of the Royal College of Physicians for recommending betablockers to patients with heart failure, which was considered dangerous at the time. Now it is recommended by NICE and GP’s are expected and incentivised to do exactly this.
In reality, very few people are going to follow a very low carb diet for practical and financial reasons. A very low carb diet (< 50g per day) is unrealistic in the general population. A low carb diet (<120-130g a day) is more sustainable.
Extreme views and practices of whatever kind are unlikely to be useful, safe or achievable in real life. As a GP and commissioner I am interested in getting the greatest amount of bang for my buck. When it comes to physical activity, the greatest health gains (and risk reduction) comes from people moving from doing nothing to doing something. When it comes to diet then from a public health perspective the greatest benefit would come from large numbers of people at significant risk of cardiovascular disease adopting a modest, sustainable reduced carbohydrate diet rather than a smaller number of people (many of whom are already highly motivated and “healthy”) adopting a more extreme, harder-to-sustain, very low carbohydrate diet.
The best medicine is the one that a person will take. The best diet is one that a person can stick to and lose weight.
That’s it for this week. The weekly Wellbeing Round up will be back next week. Until then…take care of yourselves!
