A recent study in the medical journal ‘The Lancet’ suggested that ‘Low Carb’ diets can shorten your life by 4 years. At the time myself and other nutritionists warned that there are quite a few complicated details to this study so that we felt the conclusion was somewhat misleading.
Let’s look at why…
First of all, the group who ate the fewest carbs also ate the least fibre, fruit and vegetables. Higher fibre, fruit and vegetable intake would be expected to increase lifespan. So if a person were to restrict the ‘right’ carbohydrates and not restrict these healthy ones, the results of this study would be less likely to apply to them. Another crucial point is that those with the highest carb intakes in this study also had significantly shorter lifespans (although the effect was smaller than for low-carb) than those with a more ‘normal’ carb intake.
The authors also don’t seem to have adequately considered gender and lifestyle adequately. The lowest carb group had the most men, did the least exercise and had the highest rate of smoking while the higher carb groups had higher numbers of women, did more exercise and had fewer smokers (and former smokers). These characteristics would obviously affect the relationship between carb intake and mortality. The source of macros and not just the macros consumed by the different groups also affected the outcomes of this study because the people in the low-carb group who got more of their protein and fat from non-animal sources had very significantly lower mortality. Importantly, many people would interpret ‘low carb’ as Atkins or keto (which usually contain less than 10% of calories from carbs). However, the studies reviewed by this analysis did’t look at actual “low carb” diets (below 25%) and substantial risk of mortality only increased when carbs were consumed at less than about 40%. So if your diet is 40% carbs, 30% protein & 30% fat, you needn’t concern yourself with the conclusions of this study anyhow!
Finally and possibly most importantly, everyone reacts differently to different diet and other lifestyle choices and if there is one thing science is pretty clear about, it is that there is no ideal, ‘one-size-fits-all’ diet recommendation. Some people will be fitter and healthier on low carbs, some on higher carbs!
So what this study really seems to suggest is that people should eat more vegetables, fruit and fibre, exercise more and smoke less if they eat less, perhaps especially than 40% of their calories from carbs.