Keto diets in ADPKD – what are they and do they work?

Keto diets are a hot topic in the PKD community. What are these diets and how much evidence is there that they work?

Many people with PKD are keen to do all they can to slow kidney damage and stay healthy, including following a healthy diet and lifestyle. The idea of protecting kidney health through a keto diet captures the interest and hopes of many.

With a standard diet, your body gets a lot of its energy by breaking down carbohydrates found in foods such as bread, pasta, rice and sugar. Keto diets put your body into a state known as ‘ketosis’. In ketosis, your body does not have enough carbohydrate to make the energy it needs and so it begins to burn body fat. The fat is changed to ketones which your heart, muscle, kidneys and brain can use for energy.

Ketosis can be achieved with low-carbohydrate (‘low-carb’) diets. Low-carb diets have been around for many years and include the Atkins diet, for example. Another way to achieve ketosis is to fast (not eat) for some parts of the day, or to eat very few calories on some days of the week.

Getting to grips with diet terminology

• Keto diet – any diet that causes your body to produce ketones
• Low carb – any diet with a low proportion of carbohydrates (and therefore higher proportion of fat and protein).
• Calorie-restricted – the number of calories eaten over a whole day is lower than typical or habitual but not so low as to cause malnutrition.
• Intermittent fasting – no food is eaten for a significant proportion of each 24-hour period (for example 16 hours). Alternatively, calories are significantly restricted on a couple of days of the week.
• Time-restricted – this is essentially intermittent fasting, but the focus is shifted to when you CAN eat, rather than when you cannot.

What's the evidence for keto diets?

There is some scientific evidence from animal studies that keto diets might help to protect ADPKD kidneys. In mice with PKD, reducing food intake slowed the progression of the disease (e.g., slowed cyst growth). Benefits were also seen in rats with PKD that were given a time-restricted diet or low-carb diet.

Researchers have found that some cells lining some kidney cysts die back in mice on keto diets, causing those cysts to shrink. This might explain how keto diets slow PKD progression in mice.

All these facts may have you pushing the pasta to the back of the cupboard…but we are very different animals to mice or rats. Are these results also seen in humans? This is where the scientific evidence is weak.

Two small studies have shown some promising results regarding kidney function but with a risk of side effects.

The PKD Charity’s view

The PKD Charity does not recommend a keto diet for people with ADPKD. This is because we can’t be sure there are any benefits or that these would outweigh the risks. We recommend you speak to your kidney specialist, doctor, or a dietician specializing in kidney disease before trialling any diets that differ to a normal healthy diet.

Before we can make a judgment on keto diets, a large, well-designed trial is needed that randomizes healthy people and people with ADPKD to a keto diet or to a control diet and follows them carefully for a long period of time.

For those interested, here is a summary of the findings in human studies to dates so far below.

1. A recent small study in Germany, Cukosi and colleagues compared a ketogenic diet (23 people) to a normal diet (19 people) in people with ADPKD. The diets were trialled for 3 months. 

• Over this time, the average size of people’s kidneys in the control group increased but in the ketogenic diet group decreased. While this is promising, the number of people in the study is small, and the results did not hold up to statistical analysis. There was a lot of variation between people and the results could be due to chance alone. 
• Of concern, the study found signs that the ketogenic diet trialled might not be safe for everyone. Two people on the ketogenic diet got kidney stones. Also, more people on the ketogenic diet than normal diet got slightly increased levels of fats called triglycerides and cholesterol in their blood. These fats are known to be linked to a risk of cardiovascular disease.

2. Another study has shown possible benefits of a keto diet for people with ADPKD. But there was no control group in this study meaning it’s impossible to know if the participants would have seen the same outcomes if they’d eaten a normal diet.

• The researchers asked 131 people with ADPKD who had chosen to follow a keto diet for over 6 months about their symptoms. This is a biased way to do a study because people choosing of their own accord to use these diets are likely to believe in the benefits. Nonetheless, 80% felt there was an improvement in their 'overall health' and 64% reported an improvement in ADPKD symptoms. Most lost a significant amount of weight and 64% had a reduction in blood pressure.
• More interesting still, almost two-thirds of the people had improved kidney function. In this group with an improvement, an average increase in estimated glomerular filtration rate (eGFR) of 3.6 ml/min/1.73 m² was seen between two measures taken 6 months apart. This is roughly equivalent to a 3.6% increase in kidney function. However, the remaining third of patients had a decline in kidney function or no change.
• As in the Cukoski study, some people on the keto diet got raised cholesterol. One person got a kidney stone too.

3. A group in California has designed a ketogenic diet for people with ADPKD. This is called the Ren.Nu program. Based on the theory that a diet high in carbohydrate and animal protein might speed ADPKD progression, the Ren.Nu diet is a plant-focussed ketogenic diet. No clinical trial has been done to assess the benefits or risks of this diet. Any information about the diet is currently unproven. 

What are the downsides to a keto diet?

As seen in the studies above, there is the potential for raised cholesterol and kidney stones.

In the second study above of 131 people, two-thirds of patients had periods of fatigue, hunger or ‘keto flu’. Keto flu is a non-medical term that refers to symptoms such as headache, brain fog, fatigue, irritability, nausea, difficulty sleeping and constipation that can occur within days of starting a keto diet.

Constipation can be caused by a drop in fibre. Following a keto diet can also make it hard to get sufficient nutrients if you’re not careful. Do your research and follow recommendations for the variety of foods you should have in your keto diet, including sufficient fruits and vegetables.

Keto diets are renowned for being hard to stick to for more than a few months. Even if you have improvements in kidney function while on a keto diet, we don’t know if these would remain if you switch back to a normal diet.

To conclude, the jury is still very much out on keto diets in ADPKD. More studies are underway, so we should know more soon

To find out more about other diet and lifestyle changes, see our fact sheet Diet and lifestyle in ADPKD.

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