Two years ago, a study by researcher Kevin Hall made headlines when it reported that ultra-processed foods led people to overeat and gain weight. Hall and others are still trying to figure out what makes us overdo it: At last count, 74 percent of U.S. adults and 35 percent of children were overweight or obese. And our expanding national—and global—waist-lines show no signs of shrinking. According to Kevin Hall,”We’re trying to understand the properties of our food environment that regulate appetite and cause people to overeat and gain body fat. Unlike most researchers, Hall has been able to measure precisely what people eat—and how many calories they burn. That’s because his volunteers spend several weeks living in a lab on the NIH campus. Hall’s recent studies—including his 2019 bombshell—weren’t trying to help people lose weight. “We told the participants that these were not weight-loss studies,” he explains. “We basically just put the food in front of them and said, “Eat as much or as little as you want.” Hall’s 2019 study offered 20 people largely unprocessed foods for two weeks and ultra-processed foods for two weeks.

The finding: People consumed an average of 500 more calories a day on the ultra-processed foods compared to the unprocessed foods. That led them to gain two pounds on the ultra-processed diet and lose two pounds on the unprocessed diet. Even Hall was surprised, not expecting to see such a huge effect because the meals in both diets had equal amounts of carbohydrates, sugar, fat, protein, and fiber, which are the nutrients that people have suggested as drivers of obesity. But there was a key difference between the two diets: Beverages aside, the ultra-processed food diet had nearly twice the “calorie density” of the unprocessed food diet. Calorie density is the number of calories in a given portion or a given bite of food. Studies have shown that people consume fewer calories when they’re offered foods with fewer calories per bite.

In another study, before lunch, people were given either a chicken-rice casserole with 1 1/2 cups of water to drink, or a soup made out of the casserole that included the water. Both dishes had the same ingredients and the same 270 calories. The soup including water more effectively reduced subsequent intake. Not all studies agree on the individual role of separate drinking water. In one study in older individuals, drinking two cups of water before meals helped with weight loss. But it’s likely better to consume your water that’s encompassed in food, not just drink it. When you drink water, it empties out of our stomach more quickly. But it’s not just soup. The best way to add water to your diet: eat more fruits and vegetables. In a 2007 study, women with obesity were randomly assigned to either eat less fat or eat less fat and eat more fruits and vegetables for a year. The group that ate extra fruits and vegetables lowered their calorie density more, and thus they were eating a better-quality diet. After a year, the fruit-and-veggie eaters had lost more weight (17 pounds) than the other group (14 pounds), and they reported being less hungry. This means that bulking out your diet with fruits and vegetables is a successful means to help control weight. The difference in non-beverage calorie density was huge—about 2 calories per gram in the ultra-processed diet versus 1 calorie in the unprocessed diet. This difference in calorie density may help explain why the ultra-processed food eaters ate more calories than the unprocessed-food eaters. In fact, as soon as the pandemic ends, researchers plan a protocol testing three diets that’s ready to go. Two of the three replicate the 2019 diets. That is, one consists largely of calorie-dense ultra-processed foods, and one consists largely of unprocessed foods with a low calorie density A third is a redesigned ultra-processed diet that matches the low calorie density—excluding beverages—of the unprocessed diet. If calorie density is the main driver of how many calories people eat, then the ultra-processed diet with the low non-beverage calorie density should result in a similar calorie intake as the unprocessed diet. In the meantime, Hall’s latest study added a new wrinkle. It tested two diets made largely of unprocessed foods: 1. High-carbohydrate, plant-based. Rich in vegetables, fruit, grains, and beans, it was low in fat and had a low calorie density. 2. Low-carbohydrate, animal-based. Rich in meat, poultry, fish, cheese, eggs, butter, heavy cream, and non-starchy vegetables, it was high in fat and had a high calorie density.

A popular theory about weight gain is the carbohydrate-insulin model of obesity, which predicts that if you eat a diet that’s high in carbohydrates, you’ll produce a lot of insulin after meals. According to this model, high insulin levels promote storage of calories inside fat cells, thereby starving other cells in the body of fuel, which then signal to the brain that you’re hungry so you should eat more food. But that didn’t happen, for they found exactly the opposite. The high-carb diet caused high levels of insulin after meals, but on that diet, people spontaneously reduced their usual calorie intake by about 700 calories per day, which led to a loss of about 1 ½ pounds of body fat over two weeks. It is likely that the diet’s low calorie density could have played a role in that large decrease in calorie intake.In contrast, on the low-carb diet, people didn’t eat any fewer (or more) calories than they normally did. So over two weeks, the low-carb diet didn’t lead to a significant loss of body fat. (People did lose about four pounds on the low-carb diet, but that was largely due to lost water, not body fat.) But there’s a catch: Two weeks might not have been long enough to capture what happens on a diet that’s so low in carbs that the body has to burn ketones, rather than glucose, for energy (The ketones come from both the fat that people eat and, if that’s not enough, from body fat.) When ketone levels in the blood rose and stabilized during the second week, the low-carb eaters reduced their calorie intake by about 300 per day. So they might have lost body fat if the study had lasted longer. But neither diet led to weight gain. After several studies, only one diet has led people to gain weight and gain body fat, and that’s the ultra-processed-food diet.

So how might ultra-processed food get us to overeat? Companies are all about maximizing the allure of their products,” says Michael Moss, a Pulitzer Prize-winning former New York Times reporter whose new book is titled Hooked: Food, Free Will, and How the Food Giants Exploit Our Addictions. “One definition of addiction is a repetitive behavior that some people find difficult to quit,” says Moss. “That perfectly fits our relationship to food, though it varies from person to person.” Addiction or not, it’s clear that companies keep pushing us to eat. “They hate the word addiction, but they have these euphemisms like crave-ability and likeability,” says Moss. “My favorite is ‘moreishness,’ which reflects their efforts to get us to eat more and more.” We’re easy targets for enticing food because, as we evolved, extra pounds were a survival advantage. “We’re designed to put on lots of body fat and defend against any efforts to shrink it,” notes Moss. In hunter-gatherer societies, extra body fat could make the difference between life and death. “None of this mattered until about 50 years ago, when the industry changed the nature of our food,” says Moss. How do companies take advantage of our baked-in urge to keep eating? “They want to sell as much as possible, so they have scientists who spend their time devising formulas that create the biggest attraction in the brain—the biggest wow,” says Moss. It starts with the three ingredients featured in Moss’s previous book, Salt, Sugar, Fat plus a few others, as described below:

Sugar. The industry came up with the term ‘bliss point’ to describe the perfect amount of sugar in a drink or food that would send us over the moon. Not too little, not too much.

Fat. “In snack foods like potato chips, 50 percent of the calories typically come from fat, which gives them that melt-in-your-mouth phenomenon, which so much ultra-processed food has. You hardly even have to chew it. Salt. Salt is the flavor burst because it’s often on the surface of the food and the first thing that touches the tongue.” But salt, sugar, and fat aren’t the whole ballgame. What else matters?

Fat plus carbs. Foods with high concentrations of both fat and refined carbohydrates—like chocolate, ice cream, french fries, pizza, cookies, and chips—are the foods that people find most irresistible. That might partly explain why people didn’t overeat on Hall’s low-carb diets. What’s more, flavor enhancers and texturizers might amplify the appeal of highly processed foods.

Variety. We came to cherish variety in food millions of years ago when hominids started walking upright. Variety boosted the odds of getting all the nutrients we needed. But variety still compels us. In 1982, Barbara Rolls found that people eat about 15 percent more pasta if given a variety of shapes instead of just one. And when we served sandwiches with four different fillings, people ate a third more than when they were served sandwiches with one filling. The appeal of variety explains the “smorgasbord effect.” Where you can feel completely full, but dessert comes along and all of a sudden your brain goes, “Ah, we can eat more.” When it comes to ultra-processed foods, variety can mean 10 flavors of potato chips or crackers or cereal. On the flip side, minimizing variety—for example, by cutting carbs—may help some people eat less. But it’s just really hard to maintain that strict monotony. Speed. In Hall’s 2019 study, people ate the ultra-processed foods faster than the unprocessed foods, meaning that eating rate can make a difference. Unprocessed foods often take more chewing. They have more intact fiber. They might be crunchier. They’re not blended down as much.

Advertising. Companies know how to press those emotional buttons to get us to eat, even when we’re not hungry. The key is to create strong food memories by showing the product at the precise moment when our emotions are running high. Studies show that TV ads influence food preferences and consumption, at least in children, according to the World Health Organization.

Snacking. The food industry has created more and more products that encourage us to snack during the day. It’s basically a fourth meal. Companies became very adept at ultra-convenience-that is, food you can eat while you’re doing something else. When that happens, your brain is not paying attention to the signals from your stomach that are going, “Wait a minute. I’m filling up down here.” In one study, people ate about 35 per-cent more pizza and 70 percent more macaroni and cheese while watching TV than while listening to music.

Cost. The food industry is all about making products as cheaply as possible. They use flavors that mimic the tastes and smells of the real thing. Their overall purpose is to keep their food as cheap as possible. Moss has asked companies how they’re helping people eat more fruits and vegetables. “You get this blank stare, because they can’t do it,” he says. “If they stuff a Hot Pocket with broccoli rabe, they lose the cheapness factor.”


One way to minimize ultra-processed foods and cut calorie density: load your plate with fruits and vegetables. Adding vegetables and fruits to dishes gives you bigger, more satisfying portions.. We eat with our eyes and our brains. If we see a big portion, that sets us up to feel more satisfied. If a plate looks half empty, that sets us up to feel hungry. One example: Start a sandwich with whole-grain bread, cut down on fatty meat, try mustard instead of mayo, and bulk it up with vegetables-tomatoes, peppers, onions, lettuce, whatever. You’ll end up with a sandwich that’s bigger and more likely to fill you up. Although oils, nuts, and other high-fat foods are calorie dense, you don’t have to go low fat if you eat enough fruits and vegetables, you should be eating healthy fats, and you need to bulk them up with water-rich foods. Unwilling to part with chocolate, ice cream, or other calorie-dense or ultra-processed foods you love? You need not eliminate them entirely because you’ll feel deprived. You just have to manage the portions more carefully than with fruits and vegetables. And stick with water, coffee, tea, or other calorie-free drinks. It’s easy to get rid of soda or other caloric beverages because there are so many other options. And cook your own food whenever possible. For starters, that protects you from the stratospheric calorie counts in most restaurant food, whether it’s sit-down or fast food. What you cook can be better than what’s served by the food giants. Don’t let multinational corporations dictate your diet and your health.

How Dense?

You can calculate the calorie density of any food by dividing its calories by its weight (in grams). But calories per serving also matters. Fruits and veggies are low in both.

Very Low

Calories per gram


Asparagus or cucumber—0.2

Bell peppers, green, raw—0.2

Cabbage or cauliflower, cooked—0.2

Romaine lettuce or tomato—0.2

Cantaloupe or watermelon—0.3


Broccoli or green beans, cooked—0.4


Honeydew, nectarine, or peach—0.4

Apple or orange—0.5


Plain Greek yogurt (2% fat)—0.7

Marinara sauce—0.8

Tofu, firm—0.8


Tuna, light, canned in water—0.9

White or sweet potato, baked—0.9

Shrimp, cooked—1.0

Brown rice, long-grain, cooked—1.2

Kidney or black beans, cooked—1.3

Pasta, cooked—1.5


Egg, hard-boiled—1.6


Chicken breast, roasted, no skin—1.7

Edy’s Slow Churned Ice Cream—1.8

Salmon, farmed, baked—2.1

Hummus 2.4 Mayonnaise, light—2.4

Bread, whole wheat—2,5

Ben & Jerry’s Ice Cream—2.7

Ground beef, 80% lean, broiled—2.7


French fries–3.1

Hard pretzels—3.8

Glazed doughnut—3.9


Cheddar cheese—4.0



Buttery spread, tub—4.3


Bacon, cooked—4.7

Chocolate chip cookies—4.9

Potato chips—5.3

Dark chocolate—5.5

Peanuts, roasted—5.9

Mayonnaise, full-fat—6.8


Oil (canola, olive, soybean, etc.)—8.8

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