Weight loss is big business in this country. It’s an industry that grew by about 4% last year, from $69.8 billion to $72.7 billion, according to MarketResearch.com, and is expected to grow 2.6% annually through 2023, fueled by meal-replacement products, obesity drugs, bariatric surgeries and weight-loss programs.

It’s arguably money spent unnecessarily if heeding the simple advice touted by nutrition expert Marion Nestle (rhymes with trestle) as she crosses the country talking about the challenges consumers face when food meets politics. “It’s hard for people to make sensible food choices in an environment where marketing plays a heavy role,” she said in an interview from her New York office. “Processed foods are heavily advertised, so people don’t realize how easy it is to eat healthfully. (Journalist/author) Michael Pollan summed it up in seven words: ‘Eat food, not too much, mostly plants.’”

It seems like common sense, but according to Nestle, many people have lost the ability to recognize healthful food after a couple of generations weaned on heavily processed and packaged products.

Since the 1980s, Nestle has taken on government, the food industry and the food marketing industry to bring to light their roles in the obesity epidemic and other health hazards. Nestle will give a free talk on “What to Eat: Dietary Advice Meets Food Politics” next week at the University of Hawaii’s Kennedy Theatre.

Nestle, the Paulette Goddard Professor of Nutrition, Food Studies and Public Health, Emerita at New York University and visiting professor of Nutritional Sciences at Cornell University, is the author of six award-winning books, including “Soda Politics: Taking On Big Soda (And Winning)” and “Unsavory Truth: How Food Companies Skew the Science of What We Eat.”

From 1986 to 1988, she was senior nutrition policy advisor in the U.S. Department of Health and Human Services and editor of the Surgeon General’s Report on Nutrition and Health.

In this day of hype and hyperbole, Nestle is respected for her reasoned approach to food politics. Talking to her is a breath of fresh air because she isn’t prone to hype or theatrics. When I suggest that many believe sugar is a drug, she calmly explains, “Sugar’s a food. It’s a nutrient. Plenty of people believe they’re addicted to something, but if that’s what they think, they need to be treated as an addict and get help from a 12-step program, or figure out some way not to eat it.

“If you can’t keep cookies in the house without eating the whole bag, then don’t keep it in your house.”

Nestle started her career as a nutritionist who found her current path as a crusader after attending a conference on the relationship between smoking and cancer. “It struck me that nutritionists should be doing the same thing with food.”

For a long time, she said, she couldn’t understand the confusion over how to select nutritious foods. In the introduction to her book, “What to Eat,” she wrote, “Doesn’t everyone know what a healthy diet is?”

But in talking to people across the country, she came across such comments as: “A lot of us are clueless and have no idea of how to eat,” “When I go into a supermarket I feel like a deer caught in headlights” and “I do not feel confident that I know what to eat. It’s all so confusing.”

She saw a discrepancy between nutrition knowledge and dietary behavior, largely shaped by food industry marketing and the human desire to believe a lie rather than an inconvenient truth, no matter how unrealistic.

For instance, children grow up with the knowledge than an apple is a more healthful choice than a cookie. But add the word “diet” in front of cookie and logic flies out the window as people rationalize that a diet food cannot make you fat. A person who prefers cookies to apples will find any way to believe a cookie is a viable diet choice.

Foods labeled “low-fat,” “low-calorie” or “fat-free” are targeted toward those desperate to shed weight, who are most vulnerable to the allure of an easy fix, Nestle said. If a dieter has a craving and is presented with low-calorie cookies or zero-calorie cola, he or she might gladly believe it’s fine to consume both freely — unaware that artificial sweeteners in such products contribute to obesity.

A 2016 study published in the journal JAMA Pediatrics found that mothers who frequently consumed diet beverages were two times more likely to have babies who were overweight or obese at one year after birth, compared with women who consumed fewer artificially sweetened drinks.

A 2015 study published in the Journal of the American Geriatrics Society found that people who drank diet soda gained almost triple the abdominal fat over nine years as those who drank regular soda.

“It’s a very human response to want to believe,” Nestle said. “We don’t respond intellectually to such claims, but emotionally, and marketers know that. It’s very difficult to take on a $30 billion advertising industry.”

And in light of larger social issues such as immigration and gun policy, poverty and homelessness, the every day dietary habits of American citizens aren’t much of a concern to policymakers who believe adults are capable of making their own decisions.

One would think the message would be getting across, but obesity rates in this country continue to climb. According to data from the Centers for Disease Control and Prevention’s National Center for Health Statistics, 93.3 million of U.S. adults, nearly 40% of the population, suffers from obesity based on body mass index. (Colorado and Hawaii have the lowest obesity rates, at 23% and 24.9% of the population, respectively.)

Instead of wearying of the battle, Nestle is energized by noting much has changed for the positive.

“Food has gotten a lot better in 20 years. There are more farmers markets, more opportunities to buy fresh fruits and vegetables.”

Yet, while eating was once a matter of sustenance, the rise of food media has glamorized eating a lot as a way of life, from culinary travel programs to live mukbang videos that emphasize consumption in huge amounts. So Nestle’s latest cause has been portion control.

“Portion size has gotten so much bigger over time, so it’s very human for people to want to see a lot of food in front of them,” she said. “Everyone has to have a certain amount of calories to be healthy, but many eat more than they need and that puts them at risk for Type 2 diabetes and other ailments.”

It’s up to individuals to gauge how many calories they need by using height and weight as a barometer, understand that a single fast-food meal may contain all the calories they need for one day, and adjust one’s intake accordingly.

The forumla of equal calories in and out should keep one’s weight in check. “I eat junk food, too, but I don’t eat a lot of it,” Nestle said. “It’s OK to have ice cream once in a while, and not very much.”

‘What to Eat’

Featuring nutrition expert Marion Nestle:

>> When: 6 p.m. Nov. 7

>> Where: Kennedy Theatre, University of Hawaii at Manoa, 1770 East West Road

>> Admission: Free; registration required; marionnestlehcef.eventbrite.com

>> Sponsors: Hawaii Culinary Education Foundation, with support from the College of Tropical Agriculture and Human Resources, UH-Manoa and the University of Hawaii-West Oahu Sustainable Community Food Systems Program