Labour's deputy leader Tom Watson has revealed he was diagnosed with type-2 diabetes but has "reversed" the condition through diet and exercise.
He has now come off medication after losing seven stone (44.5kg) since last summer.
He cut out junk food, starchy carbohydrates and refined sugar and took up cycling and running.
The MP has vowed to launch a crusade against diabetes if Labour wins power at the next election.
"I feel great. I feel absolutely fantastic. Chilled out, I feel like my IQ has gone up. I feel younger. It's a great feeling," he told BBC Radio 4's Today programme.
He said he developed diabetes through being "overweight, deeply unfit, [and] addicted to sugar and fast foods," and explained how he had "reversed" the condition, in an article for the Daily Express.
The West Bromwich MP - once nicknamed "Tommy two dinners" - told Today he had "battled weight since my early 20s".
"I kept putting on pounds and then I was diagnosed with type-2 diabetes. Like a lot of middle-aged men, I immediately went into denial. My condition was so frightening, I didn't begin to understand it. I just pretended I didn't have it.
"And then I hit 22 stone - and I have a young daughter. I kept reading biographies of Labour politicians who died in their 50s and I knew I had to sort it out".
After researching the subject, he started a diet by "giving up sugar" and cut out beer and curry. He then began to exercise, starting with walking then cycling, running, boxing and weight-training.
About four million people in the UK have diabetes, with the condition accounting for 10% of all NHS spending.
Poor diet and a lack of exercise mean it's possible a million more people in this country could be diagnosed with diabetes over the next 20 years, according to a report by Public Health England.
The large majority of cases - 90% - are caused by type-2 diabetes, which is linked to obesity and poor health choices.
The other 10% are type-1 diabetes, a disease of the immune system that has nothing to do with lifestyle choices and is neither preventable nor reversible.
What is type-2 diabetes?
Type-2 diabetes is a chronic condition associated with obesity and family history and is more likely to be diagnosed in older people. It's more common than type-1 diabetes.
It is caused by problems with controlling blood sugar levels - either because the pancreas does not produce enough insulin, or if a body's cells do not react to insulin as they should.
The condition is treated by medication or controlling a person's diet.
Diabetes UK offers advice on preventing and coping with type-2 diabetes.
Mr Watson has vowed to set up an independent, cross-party commission to investigate ways of preventing the condition if Labour wins power, with the aim of eliminating the estimated rise in cases within five years.
"I think a lot of people feel shame when they are diagnosed with it because you kind of know, you get warning signs," he told Today.
"But for many millions of people, it's an entirely preventable and reversible condition" with "the right nutrition and exercise".
"It is a public health scandal that so many millions of people are having to suffer this condition when they don't have to," he added.
According to a World Health Organization report, the UK is the third fattest among 53 countries in Europe, with heavy drinking a key cause.
The United Nations body found 27.8% of adults in the UK are obese compared with 32.1% of people in Turkey and 28.9% in Malta.
Those whose body mass index is at least 30 are deemed to be obese.