Diet Quality or Calories—What Matters More for Weight Loss?

Forget what you think you know about losing weight.

Medically reviewed in June 2020

The standard advice for losing weight has long been to eat fewer calories than you burn. But a new study suggests this might not paint the whole picture.

The study, published in the Journal of the American Medical Association (JAMA), suggests slashing products with added sugars, refined carbohydrates and processed junk can boost weight loss, without having to actively restrict calories or control portion sizes. Many study participants cut calories naturally by eating healthy, whole-food diets.

"The old calories in, calories out philosophy has dominated for decades, but it's a very antiquated, overly simplistic way to look at what we eat," says Darria Long-Gillespie, MD, an Emergency Department physician and Sharecare’s Senior Vice President of Clinical Strategy.

So, what does this mean for the future of weight loss? We spoke with Dr. Long-Gillespie to find out.

The study—a breakdown
Researchers conducted the year-long study to examine whether your genes help determine the best diet for you. They included 609 overweight adults between the ages of 18 and 50 and tested two diets—healthy low fat (HLF) and healthy low carb (HLC).

Participants were randomly assigned to either the HLF or HLC eating plan for 12 months. Both diets encouraged consumption of healthy, whole foods like fruits, vegetables, whole grains and lean meats, rather than processed eats. Low-fat eaters were urged to consume high-quality carbohydrates, like brown rice, whole grain oats and beans. The low-carb diet emphasized good fats, like nuts and nut butters, grass-fed animal products and fish. Prepackaged foods were discouraged, regardless of their low-carb or low-fat labels. Calories were unrestricted, and participants were urged to eat until they felt satisfied.

Although the study didn't reveal a connection between genes and your likelihood of losing weight, it did suggest something interesting: if you eat healthy, unprocessed foods, you might lose weight—and you may not even have to consciously restrict calories.

By the end of the study, most participants lost weight, and there was little difference in the amount of weight loss between the two diets. On average, HLC eaters lost 13.2 pounds and HLF dieters dropped 11.7 pounds.

Why whole foods work for weight loss
Several factors are likely at play when it comes to slimming down. For one, processed foods, especially refined carbohydrates, affect your blood sugar in a way that isn't conducive to weight loss.

Simple carbohydrates, found in white bread, pasta, bakery treats and other processed foods, cause your blood sugar to spike. As blood sugar levels rise, insulin is produced. This cycle can increase your risk for weight gain.

That's not all. "When your glucose levels rise, they very quickly plummet, making you crash and feel hungry again," Long-Gillespie says. As you reach for your next snack, your daily calorie consumption adds up.

On the other hand, whole foods are seriously powerful when it comes to keeping you satisfied. Weight loss-friendly foods—vegetables, fruits, whole grains and beans—don't contain unnecessary saturated fats, added sugars or extra calories. Instead, they're packed with nutrients, like fiber, that help keep you fuller, longer.

"Eating high-quality foods that have a combination of fiber, protein and good fats is important," Long-Gillespie says, "Not only do they tend to be rich in nutrients your body needs, they're also going to make you feel fuller and more satiated."

Still, the number of calories you eat is important. Consuming too many—even the healthy kind—can stunt weight loss and may result in weight gain. "We're not saying that calories don't matter at all, they do," Long-Gillespie says. "They're just not the end all, be all."

Healthy tips for losing weight
Infusing your diet with plenty of whole foods is a good place to start, but there are a number of other ways to modify your lifestyle to promote weight loss. Luckily, they don’t include compulsive calorie counting or swearing off your favorite meals.

Start by pushing unhealthy eats out of your diet. "The best way to do that is by replacing those highly processed foods with quality foods," Long-Gillespie recommends. A healthy diet incorporates vegetables, fruit, whole grains, lean meats and healthy sources of fat, like avocado, olive oil and nuts.

Swapping unhealthy eats with high-quality foods can be simple.

  • Opt for plain, nonfat Greek yogurt instead of mayonnaise in your tuna salad or sour cream on your chili.
  • Replace calorie-rich salad dressing with freshly squeezed lemon juice and a sprinkle of herbs and spices.
  • Blend a frozen banana with unsweetened cocoa powder as a replacement for ice cream.
  • Try almond milk and cinnamon instead of cream and sugar in your coffee. 

In addition to healthy swaps, you can also try these other slimming strategies:

  • Planning healthy snacks is a good way to prevent reaching for unhealthy vending machine treats or overeating at your next meal. Keep your energy levels up throughout the day by preparing a handful of almonds, air-popped popcorn, baby carrots and mashed avocado or a banana and natural peanut butter. 
  • Food journaling helps you keep track of the foods you eat throughout the day, making you more aware of your choices. A 2011 review of 22 studies suggests those who track their weight, food and activity are more successful at losing weight and maintaining weight loss. To keep tabs on your diet, use a handwritten log or a phone application, like Sharecare, available for iOS and Android.
  • Munching mindfully can make you more aware of how much and what types of foods you're putting in your body, keeping you from chowing down in front of the television or computer. Research suggests it can help you slim down.
  • Getting more daily physical activity can be tough, but it's beneficial for overall health, and can help boost weight loss. National guidelines recommend 150 minutes of moderate-intensity physical activity or 75 minutes of vigorous-intensity physical activity weekly. If you're trying to lose weight, shoot for more activity. Adding extra steps to your day—like walking to work, taking a stroll on your lunch break or skipping the elevator—can help.

If you’re looking to slim down, you needn't throw caution—or calories—to the wind, but focusing your attention on whole foods is a good place to start.

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