Emerging evidence supports the use of the ketogenic diet against a variety of neurological disorders including multiple sclerosis and Alzheimer’s. But what about Parkinson’s? Is there a potential place for the ketogenic diet and could following this pattern of eating improve symptoms of Parkinson’s and your quality of life? Before looking at the evidence let’s first take a closer look at the ketogenic or keto diet.
What is the keto diet?
The keto diet is a very high-fat, very low-carbohydrate, moderate protein diet that induces nutritional ketosis. Nutritional ketosis occurs when your body starts burning fat instead of carbohydrate for energy. Burning fat for energy produces ketones. Ketones are water-soluble compounds that can cross the blood-brain barrier to provide an alternative source of energy to the brain. Most people will need to eat less than 50 grams of carbohydrate per day to reach ketosis.
Researchers suggest the keto diet may help with diminished mitochondrial energy metabolism. In Parkinson’s the potential support for the keto diet comes from a few human studies.
Study 1 – Vanitallie et al.
The first study, conducted in 2005, assigned 7 participants with Parkinson’s to the keto diet for 4-weeks to determine if symptoms could improve on this diet. 5 participants completed the study. Urine ketones were measured daily. The macronutrient breakdown as a percent of total calories was 90% fat, 2% carbohydrate and 8% protein.
Outcomes: Unified Parkinson’s Disease Rating Scale (UPDRS) scores improved in all 5 participants. Among symptoms that improved were resting tremor, freezing, balance, gait, mood and energy level. Although 2 participants did not follow the diet as strictly as others, they were still able to achieve ketosis and improve UPDRS scores. All participants had a body mass index above 28 and lost an average of 6.1 kg during the study period.
Limitations: the assigned diet was inadequate in protein which may have improved levodopa absorption making it difficult to determine if the observed improvements were due to this or due to the effects of the diet. In addition, there was no control group, a very small sample size was followed for a short duration and the potential of a placebo effect must be kept in mind when interpreting these outcomes.
Study 2 – Phillips et al.
The second study, conducted in 2017, randomised 47 participants with Parkinson’s to either the keto diet or low-fat diet for 8-weeks to determine if symptoms could improve on either diet. 38 participants completed the study. Blood ketones were measured daily by both groups. Each diet was designed to provide a similar amount of calories and protein. Protein intake was approximately 1 gram of protein per kilogram of body weight per day. The keto diet contained 75-80% of total calories as fat whereas the low fat diet contained 20-25% of total calories as fat.
|Low-fat diet (per day)||Keto diet (per day)|
|42 grams fat||152 grams fat|
|-10 grams saturated fat||-67 grams saturated fat|
|279 grams total carbohydrate||27 grams total carbohydrate|
Outcomes: both groups showed small but significant improvements in motor and non-motor symptoms. Those on the keto diet experienced a greater improvement in non-motor symptoms especially for urinary problems, pain, fatigue, daytime sleepiness and cognitive impairment. The average participant in both groups lost 4-5 kg but remained overweight at week 8.
Limitations: the group on the keto diet experienced a transient exacerbation of tremor and/or rigidity which resulted in 2 participants dropping out of the study after week 1. This adverse effect was improved or resolved in many participants in weeks 5 to 8. Study authors speculate the abrupt change in fat intake may have accounted for this effect.
The observed weight loss may have contributed to the improved motor scores in both groups. In addition, a small sample size was followed for a short duration. It’s also important to note that the keto diet in this study contained 11 grams of fibre which is inadequate.
Study 3 – Krikorian et al.
The third study, conducted in 2019, aimed to investigate the effects of a low carbohydrate, ketogenic intervention on cognitive performance in participants with Parkinson’s disease-associated mild cognitive impairment. 14 participants with Parkinson’s were randomised to either a high-carbohydrate or low-carbohydrate diet for 8-weeks. Ketone levels were measured during weeks 2, 4 and 6. Each diet provided a different amount of calories and protein. A target of 20 grams of carbohydrate per day was provided for the low-carbohydrate group.
Outcomes: the low-carbohydrate group demonstrated enhanced cognitive performance in aspects of executive ability and memory. There was no benefit observed for motor function in this trial.
For those on the low carbohydrate diet, calorie intake declined significantly with reductions in weight and waist circumference observed. In contrast, these measurements were unchanged for those on the high-carbohydrate diet.
Limitations: the short duration of the trial and small sample size were limitations noted by the authors who also suggested benefits in motor function may have been observed with a longer intervention period.
The observed change in body weight was strongly associated with cognitive benefit.
The low-carbohydrate group had a higher protein intake compared to baseline which may have affected how well levodopa was absorbed in these participants. Both diets in the trial lacked fibre, in particular the low-carbohydrate diet contained only 6.8 grams of fibre per day.
Based on these studies, it’s unclear what the ideal ratio of fat to carbohydrate would be most appropriate for people with Parkinson’s to improve symptoms. In general, the amount of carbohydrate required to achieve and sustain ketosis varies from person to person. Rather than following a clear-cut or strict ratio perhaps focusing more on achieving ketosis is required. This was evident in the first study where 2 participants achieved ketosis and saw improvements despite following a less rigorous diet.
Is the keto diet right for me?
The keto diet can cause appetite suppression and as seen in all 3 studies weight loss. For some people with Parkinson’s’ who are carrying extra weight this may be appropriate but for many struggling with poor appetite and unplanned loss of weight this dietary pattern may not be suitable.
The keto diet is very high in fat. If you suffer from gastroparesis or slow stomach emptying consuming very high-fat meals can cause symptoms such as nausea, stomach pain and bloating. As fat empties more slowly from the stomach this dietary pattern may not be suitable.
What about side effects on the keto diet?
It’s important to note that the keto diet can have side effects. The most common include nausea, vomiting, headache, fatigue, dizziness, insomnia, difficulty in exercise tolerance and constipation. These side effects usually resolve in a few days to a few weeks. Ensuring adequate fluid and electrolyte intake can help counter some of these side effects.
Nutritional ketosis is considered quite safe as ketones are produced in small concentrations. It greatly differs from ketoacidosis which is a life-threatening condition resulting from dangerously high levels of ketones and blood sugars. Ketoacidosis mostly occurs in people with type 1 diabetes whose bodies do not produce any insulin. It can also occur in individuals with type 2 diabetes who have little or no insulin production. Several things can lead to ketoacidosis including illness, improper diet or not taking an adequate dose of insulin.
Where to from here…
If you have done your research and want to commence the keto diet, check with your doctor first as this dietary pattern may not be suitable for you. If you have diabetes and take insulin or oral hypoglycaemic agents, you may need your medications adjusted before initiating this diet. With diabetes, you should regularly monitor your blood glucose and blood ketone levels and liaise regularly with your doctor.
If you do decide to start the keto diet, trial it for a few months and closely observe your symptoms. Your doctor can monitor blood-work, including your blood lipid profile, and potential side effects.
You should also work with a Dietitian to ensure you follow a well-formulated keto diet containing nutrient dense foods. In addition, be sure to reduce your carbohydrate intake gradually and increase your fat intake gradually over several weeks. You can test your blood ketone levels using a device, such as this one, available online or from a pharmacy. Alternatively, urine testing strips can also indicate ketone levels.
If after giving it a go, you decide the keto diet is not right for you, transition back to your usual diet gradually and stay in contact with you doctor.
The keto diet is a very high-fat, very low-carbohydrate, moderate protein diet which has been shown to improve certain symptoms of Parkinson’s in a few small studies. However, due to a lack of long-term studies it’s premature to make a general recommendation that people with Parkinson’s should follow the ketogenic diet. It may be that the keto diet best suits people with Parkinson’s who are overweight with metabolic syndrome, insulin resistance and/or type 2 diabetes. However, further longer and larger studies are required investigating the long-term health implications of this diet.
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Krikorian R, Shidler MD, Summer SS, Sullivan PG, Duker AP, Isaacson RS, Espay AJ, available online 6 August 2019, Nutritional ketosis for mild cognitive impairment in Parkinson’s disease: A controlled pilot trial, Clinical Parkinsonism & Related Disorders.
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