High-protein diets such as the Atkins diet have been used by many people worldwide to help shift unwanted weight.
But while such diets can be effective, there have been concerns that following them for a prolonged period can cause kidney damage in some at-risk groups, such as people with type 2 diabetes, as the body can have trouble eliminating high volumes of protein waste products.
New research, however, suggests that a low-carb, high-protein diet might actually improve kidney function in some cases.
The idea behind these diets is that protein (such as meat, fish and eggs) and fats boost your metabolism, and are more filling, which means you consume fewer calories.
New research suggests that a low-carb, high-protein diet might actually improve kidney function in some cases
However, for the 4.9 million people in the UK with diabetes — the vast majority type 2 — high-protein diets could be a real problem as around a third of patients also have some degree of kidney disease (caused by high blood sugar levels damaging the blood vessels in the kidneys).
In 2019, Professor Denis Fouque, former chair of the European Renal Nutrition Working Group, which carries out research on the effect of lifestyle and diet on kidney health, warned a high-protein diet ‘may boost a pre-existing low-grade chronic kidney disease which is often prevalent in people with diabetes’, and that it might even increase the risk of new cases of kidney diseases. Yet recently, studies have shown that a low-carb (less than 130g a day), higher-protein diet can actually be beneficial for people with type 2 diabetes.
It could even reverse their condition, as one study, published last year in the journal BMJ Nutrition, Prevention and Health, suggested.
When patients with type 2 diabetes followed a low-carb diet for 23 months, 46 per cent reversed their condition and no longer needed to take medication.
Now, a study, published today in the journal Current Opinion in Endocrinology, Diabetes and Obesity, suggests that previous concerns about high-protein diets causing kidney damage are unfounded.
In the study, Dr David Unwin, a GP in Southport, Merseyside, analysed the records of 143 type 2 patients who had followed a low-carb diet — an approach he has been offering since 2013.
The patients (who have an average age of 61) had been diagnosed with diabetes for an average of five years and three months. They had normal kidney function or mild kidney disease and had followed a low-carb diet for an average of 30 months.
A previous study showed that this group lost an average of 9.5 kg, and 47 per cent reversed their condition. In the latest study, two thirds of these patients also had improved kidney function.
In addition, estimated glomerular filtration rate (which measures kidney function) improved by 2.4 units over the time frame (a drop of 2.5 was expected). Two other markers of kidney health also improved — one by 64 per cent.
This is contrary to what might be expected with older people who have type 2 diabetes, says Dr Unwin, due to the effects of the disease and the fact that our kidney function decreases with age.
Dr Unwin and his co-author Professor Chris Wong, a consultant nephrologist from Liverpool University Hospitals Foundation Trust, believe the improvement is down to better blood sugar levels (which reduce pressure on the kidneys) and blood pressure.
‘We suspect high blood sugar is central to the damage that people with type 2 diabetes experience to their kidney function, so reducing blood sugar levels seems to be a logical first step,’ says Dr Unwin.
However, it’s unclear whether this approach would help those with type 2 diabetes and moderate or severe kidney disease.
Furthermore, a low-carb diet is not without its downsides. A review in the journal Nutrients in 2019 concluded ‘few data are available about sustainability, safety and efficacy in the long term’.
In May, the charity Diabetes UK recommended a lower carb diet ‘as a short-term effective option for adults with type 2 diabetes who have obesity or are overweight’, but added there is ‘no consistent evidence that a low-carb diet is any more effective than other approaches in the long term’.
Dr Duane Mellor, of the British Dietetic Association, says the idea that protein needs to be restricted is wrong. ‘For someone with healthy kidneys, protein is not a problem, and for people with kidney disease it’s important not to restrict protein too much as it can lead to malnutrition,’ he says.
‘It’s likely that if you lose some weight and have improved glucose control, kidney function will improve a bit, but this study doesn’t prove this. More research is needed.’