One of the most common questions I get asked as a personal trainer, and one that I see often comes up in the fitness realm is: Can high protein diets cause damage to your kidneys?
With so many claims telling you to do this and that, it can all get a little confusing, so I’m here to help you separate the fact from fiction. Let’s look at understanding where this idea came from, and what science says.
You may have heard at some point, whether that’s online or maybe even seen in the papers, the claim that eating too much protein will damage your kidneys and can be harmful to your health. This idea was popularised from a study which investigated patients with pre-existing chronic kidney disease. For this specific patient group, those that were on high protein diets experienced strain on the kidneys so a low to moderate protein intake would be recommended for these patients. It appears that from this finding on this specific population group, the media has generalised and brought this idea that high protein diets can cause kidney damage to our attention.
So does a high protein diet impact kidney function on healthy individuals?
In a healthy individual, an increase in protein intake will lead to an increase in filtration rate and glomerular pressure (ie. how well the kidneys are working to remove waste products from the blood). This is thought to be a normal adaptive process but has shown no detrimental impact on renal function. Even when looking at ‘at risk’ groups, such as the obese and hypertensive patients, studies have also shown no loss of renal function, or any indications that following a high protein diet will cause any damage to people with normal renal function.
The same study also mentions athletes regularly consuming in excess of 2.0g/kg protein (The RDA is 0.8g/kg) show no signs of being any more at risk than the rest of the population, despite the possible high intake daily. Further to this, research carried out by Antonio et al 2016 2 showed no negative impact on health markers in resistance trained men, of whom were consuming a diet in excess of 3.0g/kg of protein daily (significantly higher than most protein diets and certainly higher than any intake previously personally recommended), after 4 months.
At present, there are no long-term studies considering the effects of high protein intake and renal damage in healthy individuals.
In addition to there being no proof of kidney damage as a result of a high protein diet (the definition varies from study to study, however, anything over 1g/kg could be ‘high protein’) in individuals with normal renal function, many studies have shown that, when it comes to weight loss, higher protein diets can be significantly beneficial to successful outcomes. This is due to the effects of protein on increasing satiety and requiring proportionally more energy to digest. Based on this, it’s safe to say that the chances of damaging your kidneys by eating too much protein is very small, provided you are a healthy individual. If you are do have kidney disease, you should speak to your GP for advice.
So how much protein should I eat?
How much protein you need will be dependent on multiple factors. Current guidelines for the RNI (reference nutrient intake) of Protein is set at 0.75g per KG bodyweight per day. Current research is leaning towards the suggestion that this should be higher, maybe closer to 1g per KG bodyweight per day. But it is important to note that the RNI is regarded as the essential amount to remain healthy, rather than the optimal amount.
Many studies show that use of higher daily protein is beneficial in terms of helping to retain muscle mass whilst dieting, improving satiety, and optimising muscle gain. Most people do well with between 1.4-2g/kg/day. Higher amounts have been studied but it becomes harder to hit such targets, bloating can be an issue, and the benefits beyond this don’t seem as substantial.
Plus, as we age it becomes more difficult to build and retain higher muscle mass (roughly 1%/year decline after peak), and in women there is a significant decline post-menopause. Therefore it becomes more important to ensure sufficient protein intake – so you should look at optimising how much we need to eat.
Tips on how to know you’re consuming enough protein
To be sure, make sure that you have a good amount of a protein source at each meal (aim for at least 25g/meal as a minimum). Or use your hand for a rough guideline. A palm sized amount of a lean meat or fish is a rough estimate for what 1 serving (20-30g) is equivalent to, so for women 1 serving, and for men 2 servings would be more appropriate.
This is obviously very individual, so depending on your size, weight etc you will need more or less. Use of a protein shake can be beneficial to help you reach your targets, but is by no means essential. Consider it a performance food rather than a supplement.
Other methods: you can track your protein intake if you have a target to hit, using an app, checking the packaging of the food you eat or the old-fashioned way with pen and paper. Photographing what you eat can also be a good way of self-checking.
It’s hard to ‘know’ exactly how much protein you need but unless you are eating a very low amount you won’t see any detrimental health effects. Recovery time can be an indicator. You may find that if you eat a higher level of protein, you will be able to recover a little faster. Try to track or gage how much protein you are consuming and based on your consumption, check in with how you are feeling and how your performing in your training, and make amendments if required.
To help you get your protein in, here are some healthy protein sources you can eat:
Lean Meats and Fish
Whey Protein (V)
Cottage Cheese (V)
Greek Yoghurt (V)
(beans, seeds, nuts) (V) – but be aware that some of these are high fat, so to get the required protein from vegetarian/vegan sources can be challenging without consuming a lot of calories.