Like a lot of new physicians, a busy residency left me with little time for exercise or a balanced meal. I'd never been overweight, but suddenly my waistline was expanding.

But I wasn't too worried – after all, I was only in my 20s. What could a few temporary pounds do to hurt me?

It was a story I had often heard from patients, only now it was playing out in my own life.

But to my surprise, I learned at a routine checkup that I had prediabetes – elevated blood sugars – that can eventually progress to diabetes if untreated. Over time, without proper management, diabetes can take a toll on your entire body. It can ravage your nerves, take your limbs, imperil your kidneys, clog your arteries, and render you blind. There are few other diseases as destructive as diabetes and fewer as common. Diabetes already affects nearly 30 million Americans with another 84 million, or a third of adults in America, having prediabetes. Ninety percent of those with prediabetes don't even know they have it.

Type 2 diabetes is the most common form of diabetes, comprising 90 percent of all diabetes cases in the U.S. The less common form, Type 1 diabetes, is an autoimmune condition that usually, but not always, starts in childhood. Type 2 diabetes is a byproduct of insulin resistance, meaning that insulin works less effectively, so you need more of it.

And while it is true that the risk of developing Type 2 increases with age, we are seeing more people younger than I was, even children, with what once was called "adult-onset diabetes."

How did I reverse my own prediabetes?

I forced myself to find time for exercise and better nutrition. Fruits and vegetables became my friends in my new plant-based diet, and so did a smaller waistline, and normal blood sugars.

Sounds simple, but these are not easy changes to make. Making it even more difficult is that patients with diabetes get so many conflicting messages, they can be left defenseless against the torrent of sugar coursing through their arteries. For instance, patients who fear dietary sugar tell me they avoid fruit in favor of savory foods like a ham sandwich. Yet their high blood sugar persists because they don't realize they are sabotaging themselves.

Most whole fruits – consumed with all the fiber rather than strained into juice – are some of the healthiest foods a human can eat, diabetic or not. In a recent meta-analysis, people who ate more fruit were shown to have a lower risk of developing diabetes. For those that already have diabetes, eating whole fruit was associated with reducing the risk of health complications, including death.

But when fruit is turned into juice, it acts like any other refined carbohydrate, which all diabetics should truly avoid.

However, too many people confuse refined carbohydrates with all carbohydrates. Carbohydrates are important and when eaten in an unrefined form – as whole grains, fruits, vegetables, potatoes, beans, and lentils – can lead to improvements in diabetes.

Consider that ham sandwich. The bread, especially if it's a refined white bread, affects blood sugar just like candy would.

Nor is just eating ham the answer. Too many of my patients view carbohydrates in any form as diabetic kryptonite, and instead consume foods that are high in saturated fat, like red meat and processed meat, further increasing the risk of diabetes. Even high consumption of fish, despite its health allure, has been linked with a higher rate of diabetes development.

When whole-food, plant-based diets have been compared to traditional diets prescribed for diabetes, they have tripled the reduction in sugar levels in diabetics. These types of diets also have the advantage of helping people with other common conditions, including heart disease and cancer.

The holidays are often seen as an excuse for dietary indiscretion, but the impact unfortunately lasts far longer than the celebrations. Several studies have found that the typical holiday weight gain is "only" a few pounds, which can accumulate and increase the risk for diabetes. Yet in a summary article released this year, researchers found that the weight gained during the holidays represents more than half the weight gained annually – and is not lost over the following year, leading to permanent weight gain.

The situation would be hopeless if it were not for a whole-foods, plant based diet, which has been shown to help you lose weight and treat diabetes simultaneously.

In 1925, Frederick Banting, the co-discoverer of insulin, warned humanity during his Nobel Prize lecture, "Insulin is not a cure for diabetes; it is a treatment." This holiday season, more than 90 years later, we would be wise to ask for healthier, plant-based options and not for more insulin.

Dr. Shivam Joshi is a lifestyle physician and nephrology fellow in Philadelphia. Follow him on Twitter @sjoshimd.