Dr. Kevin Gendreau lost 125 lbs. by taking a three-pronged approach.

The major components were: finding the proper motivation, a whole food diet without processed carbohydrates and intermittent fasting, the Fairhaven, Mass. primary care physician tells PEOPLE.

Unfortunately, the motivation came with tragedy. “When my sister was diagnosed with an aggressive, rare form of cancer, I decided to change my life,” said Dr. Gendreau, who had reached 300 lbs. by consuming “a diet full of bread, pasta and chips.” “For me, being obese was a choice. How could I literally eat myself to death while my poor sister was fighting for her life?”

After being diagnosed with hypertension, high cholesterol, diabetes, sleep apnea, plantar fasciitis and fatty liver disease in 2016, Dr. Gendreau, 30, finally decided to make a change.

He came to the realization that he had been “an emotional eater” following stressful years including the loss of his father and the challenges of medical school.

“Once I made the black-and-white decision to stop being unhealthy, everything else just fell into place,” he said. He switched to a high fat, low carb diet and started tracking his progress through MyFitnessPal.

“As my sister’s condition worsened, I became more motivated than ever to eat healthfully because I knew my niece [Sophia, now 7] and nephew [Henry, now 3] would need me to be at my best,” said Dr. Gendreau. Sadly, his sister passed away in June 2017.

The new regime centered around very specific foods including fruits, vegetables, nuts, chicken, turkey, fish, eggs, non-fat Greek yogurt, olive oil, balsamic vinegar, and non caloric spices and seasoning.

“If it’s not on that list, I don’t eat it,” said Dr. Gendreau, who also shares his before and after photos on Instagram and Facebook. “It’s astonishing to see how quickly and permanently you can lose weight with a whole food diet like this.”

After his weight hit a plateau, he turned to intermittent fasting after reading and learning more about it from The Obesity Code.

“Intermittent fasting works because it helps naturally decrease your daily calorie consumption while improving your insulin sensitivity,” said Dr. Gendreau, who eats from only 12pm to 8pm every other day. Outside of that window he allows himself black tea, black coffee and water. The 16-hour fasts helped him shed the last 50 lbs. of the 125 lbs. he lost.

He even began recommending his routine to patients. “Intermittent fasting has been life changing for many of my pre-diabetic and diabetic patients,” Dr. Gendreau said. But he cautioned, “Intermittent fasting is safe for most people, but not everyone. You should definitely talk to your own doctor before starting any diet or exercise plan.”