Don't call this science as it's my anecdotal report of an informal study of 1, myself.
SBMA aka Kennedy's disease has symptoms most similar to ALS aka Lou Gehrig's disease but a much slower rate of progression. Progression can be so slow that some with the disease live a full life though many die young from things old people die from such as heart attacks, stroke and pneumonia. SBMA is one of 9 known polyglutamine (an expanded CAG repeat) diseases and the one with the weakest correlation between repeat length and the severity/rate of progression.
Last April, at 52, I expected to die soon. A friend with the disease, 1 year older and eerily simiilar to myself as if my brother, died from a stroke. My blood pressure was sky rocketing despite medication.
At 40 I could still eke out slow grueling 100 mile bike rides. But despite my efforts to slow the disease through exercise and diet - going vegetarian, almost vegan, increasingly avoiding any fat, especially saturated fat, by 52 I gained 15 lbs while losing another 30+ lbs of muscle. I could still stand and walk a few feet but would fall several times each day and my neurologist had been trying to get me to give up on the idea of walking to save me serious injury after numerous minor injuries & fractures, etc.
I began an aggressive diet in May. I was eating roughly 2000 calories/day roughly 80% carbs and 10% each protein and fat. I had been increasingly suffering symptoms of diabetes for years despite my fasting blood glucose never going over 130 and my doctors saying that showed I wasn't diabetic. But I wasn't convinced and after some reading I decided to go cold turkey on all high glycemic carbs, nothing with added sugars, no bread, no fruit juice, etc. which dropped me to ~1000 calories/day.
I lost 10 lbs in a month and was feeling better when I was warned to slow weight loss to 1 lb a week as a rapid release of fat sequestered toxins could aggravate my neuro degeneration. Starting to question the wisdom of a high carb almost vegan diet I added back about 600 calories daily, mostly fat and protein adding grass fed meat and dairy to my diet and I continued improving.
A month later a new study on my disease was published. It was done in Italy on mice engineered to express my diisease aggressively with a very high repeat count. They put some of these mice on a "high fat diet" (45% fat...) and they lived TWICE as long as mice on the standard mouse chow diet with far less wasting.
After more reading I decided to throw caution to the wind and transition to a keto diet. I've made many other changes and I don't know how big a factor dietary changes have been in my recovery but I now expect to live a full life.
All of my most aggravating medical conditions are abating. I've stopped taking any medication. My blood pressure is good, HDL up 250%, triglycerides less than half, CRP and HbA1C each down ~25%, weight down 35+ lbs while gaining several lbs of muscle, etc. I've resumed walking, biking, swimming and weight training and have been making gains in each. I'm looking forward to adding jogging and dancing and I've never been able to dance.
I've told researchers studying my disease my story and while there was modest interest mostly I was cautioned to be more careful and discontinue my experimentation with an unproven dangerous diet. And this is despite a lot of recent research indicating that my disease has a major metabolic component, that muscle wasting actually precedes neurodegeneration, that insulin insensitivty, dyslipidemia, NAFLD, etc. are all significantly elevated and genes involved with glucose metabolism in skeletal muscle are markedly down regulated with SBMA.
There's still no approved treatment for my disease and research is focused on finding a pill. I'm focused on attaining as far as possible a body builder's physique to hopefully inspire others with my disease to stop waiting for a safe pill like the recently trialed BVS857 which caused an immune response against both the drug and one's insulin, and instead try a dangerous diet.