David Kessler has been fighting the weight wars his entire life. “I own a suit in every size,” he says. Kessler, 68, former commissioner of the Food and Drug Administration, is convinced people gain weight because they eat not only more calories than they burn but also the wrong things, namely many kinds of processed foods.

Kessler has a new book out, “Fast Carbs, Slow Carbs,” with research arguing that certain processed foods — specifically those with wheat and corn — cause us to overeat, gain weight and become ill. The wheat and corn in these foods typically has been processed into starch — which, he says, is the villain behind weight gain.

He has switched his own eating habits as a result, avoiding these “fast carbs,” among them flour, baked products such as breads, cakes and cookies, as well as cereals, pizza, and snacks, such as chips and crackers. The clue, he says, is to read labels and shun products where the main ingredients are wheat or corn.

Instead, he now turns to “slow carbs,” foods that are “structurally intact,” such as fresh fruit, cruciferous vegetables like broccoli and cauliflower, asparagus, bell peppers, and tomatoes, all high in fiber and with little starch. Also, legumes — beans, lentils and chickpeas — are good, even though they contain starch. The starch in these, however, typically is trapped within fiber, making it harmless, he says.

“Certainly, this is the same advice we’ve been hearing for years and it remains sound,” he says. “However, now we are looking at food through a different lens.”

Starch is the “lens” he is referring to — a white, powdery, tasteless substance contained in many processed foods. It results when food manufacturers mill, puff, pop and otherwise refine wheat and corn, stripping out its natural structure, which makes it rapidly absorbable in the body.

Starch is pervasive in the majority of processed foods we eat, he says, a long list of all the things we crave: fries, pizza, cookies, cakes, crackers, even gluten-free foods. He says eating them enables people to add pounds almost effortlessly. Starch, essentially, floods the body with large quantities of glucose (sugar) that are rapidly digested by the body. Moreover, starch is a delivery device of harm — it carries fat, sugar and salt.

“Ultra-processed foods are designed to be irresistible and encourage overeating,” Kessler says. “Processing enhances palatability by adding sugar, fat and salt. Once we start eating them, it’s almost impossible to stop. Our gastrointestinal tracts rapidly absorb fast carbs, and, as a result, our bodies don’t feel full. So we keep eating, and gain weight.”

More important, fast carbs also promote insulin resistance, meaning the body can no longer regulate blood glucose. Insulin is a hormone the body produces to move glucose into the cells, which use it for fuel. When insulin cannot do this, sugar builds up in the blood and, over time, can harm the small blood vessels in the heart, kidneys and eyes.

This, in turn, can lead to metabolic syndrome, a constellation of symptoms that include hypertension, high blood sugar, excess body fat around the waist and abnormal cholesterol or triglyceride levels. Metabolic syndrome raises the risk of developing Type 2 diabetes, stroke, heart disease and other serious conditions.

“People need to realize that starch amplifies the effects on our bodies,” he says. “It’s destroying our bodies.”

When people struggle with their weight, they often blame themselves.

“They think it’s them — that it’s their fault — and get very frustrated,” he says. “They don’t like themselves because of what they have a hard time resisting.”

Nearly half of all American adults are obese, and almost one-tenth are severely obese, according to the Centers for Disease Control and Prevention. Moreover, both have increased since 1999, the CDC says. The agency says that obesity also now affects 1 in 5 children.

For years, most experts believed fat, sugar and salt were the killers in American diets. This is still true, but it’s more complicated, Kessler says. A decade ago, he wrote about the threesome’s addictive qualities in “The End of Overeating,” pointing out how eating foods overloaded with fat, sugar and salt contributes to obesity.

His latest book builds upon that evidence, essentially connecting their relationship to starch, arguing that by cutting out many processed foods, we can curb starch intake and the dangerous substances they transport.

That doesn’t mean that foods without starch — but that contain sugar, salt and fat — are okay; their dietary dangers haven’t changed, he says, one reason he also avoids sugar-laden puddings, ice cream and sweetened sodas.

Nevertheless, eliminating most processed foods will limit the intake of fat, sugar and salt, he says, adding that, until now, starch has been overlooked in the dietary debate.

“Everyone knows fat, sugar and salt are bad for you, but no one paid any attention to starch,” he says. “That’s the story we missed.”

Kessler began to view processed foods with suspicion during a San Francisco supermarket excursion in 2017, when he paused to scrutinize the label on a cereal box.

“I wondered what was in the box,” he recalls. “It didn’t say ‘starch.’ It said ‘wheat.’ I started talking to scientists and people who worked in industry, and realized that the processing techniques really pummel the intact nature of wheat in a major way. If you look at the cereal in your bowl, it looks nothing like wheat. The mechanical forces have changed it. What’s in that box are short chains of glucose — which is sugar.”

To be sure, right now we are living in trying times. The novel coronavirus pandemic has confined most of us to our homes, forcing us to become dependent on home grocery deliveries, takeout orders and abbreviated shopping trips. Many foods are out of stock, including nutritious ones. It’s also when we often seek “comfort” foods to ease our anxiety, many of them unhealthy.

“If you want to understand the power of food, there is no better time than now,” he says. “People reach for fat, sugar and salt because these foods are comforting. I understand this. When I get stressed, I fall off the wagon. It’s very important now that we don’t deprive people of comfort. But try your best. You actually may have the time now to focus on it. If you can’t get what you want from the supermarket or home delivery, take it as an opportunity to shift your diet. Hopefully, when this is over, we will realize how much we want to stay healthy.”

He points out that not all processed foods are bad — cereals such as steel cut oats, rolled oats (but not instant or “ground” oats) and muesli are good — while some unprocessed foods — white potatoes and white rice — contain natural starch, making them rapidly absorbable — and not so good.

Moreover, some foods touted as “whole grain” may not be as healthy as we think. There are some that have intact whole grains, but there’s no way for consumers to know by reading the label which ones they are, he says.

“Many still are processed carbs with the bran added back, which are still rapidly absorbed,” he says. Rather than breads, he suggests consumers try to eat such whole grains as steel cut oats, brown rice and quinoa.

Finally, he says we should teach kids at an early age — before they can head to the vending machines — how foods are made, and how they affect the body.

“Maybe this would make it easier for them to reach for slow carbs instead of the fast ones, despite the temptations,” he says. “It would be one of the greatest gifts we could ever give them.”