Low-carb diets: an expert explains how they work and if they’re right for you

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Carbs are a popular villain in diet culture, often used as a catch-all term for any unhealthy-but-delicious fare you might indulge in. Even if you haven’t tried a low-carb eating plan, you’re probably somewhat familiar with the concept of cutting bread, pasta, and potatoes, for weight loss and/or to lower blood sugar.

Although this way of eating can be effective, it’s not a magic bullet—and carbs as a category aren’t the enemy, says Caroline Susie, registered dietitian and national spokesperson for the Academy of Nutrition and Dietetics. 

“There are so many wonderful qualities about carbs—they’re really the preferred energy for our brains and body,” she says. And because of the diet industry’s tendency to demonize the whole group, sometimes the baby gets thrown out with the bathwater.

“When you take away foods like beans that offer you a lot of fiber, or if you take away fruit, you’re lowering your fiber intake and your vitamin and mineral intake, and there’s a higher potential to be at risk of certain deficiencies,” she says.

You should always talk to your doctor before dramatically altering your eating patterns to be sure you’re meeting your nutritional needs. But if low-carb eating gets the green light, be sure you take on your new food plan with these considerations in mind.

How low should you go?

The USDA’s Dietary Guidelines for Americans recommends that 45%–65% of your daily calorie intake come from carbohydrates. For a 2,000 calorie-a-day diet, that translates to about 900-1,300 calories of carbohydrates, or 225–325 grams of carbs. Low-carb eating patterns typically limit carbs to 26% of your daily calorie intake, or fewer than 130 grams of carbs per day on a 2,000 calorie diet.

But before you take that number and run, it’s important to consider your unique physique. Online calculators such as the National Institute of Health’s Body Weight Planner and the USDA’s MyPlate Plan can give you personalized calorie counts best for your stature, age, and fitness level, and tell you from which food groups you should get those calories. But even then, Susie says there’s more to take into account to ensure you’re eating wisely.

“We’re all more than just our age and gender and height and activity level, so it’s imperative that you take health conditions into consideration,” she says. For example, your needs will vary if you’re pregnant or breastfeeding, or if you’re living with diabetes.

Types of low-carb diets

While there is no end to different brands and methods of low-carb diets, they essentially fall into one of two broad types: those that lower carbs and raise fat, and those that lower carbs and raise protein.

Low-carb, high fat diets, such as the keto diet, focus on fat-rich foods that can serve as alternate fuel once your body uses up your curtailed number of carbohydrates. A typical breakdown for a 2,000 calorie per day diet on a keto plan would be 70–80% fat, 5-10% carbohydrate, and 10-20% protein, or around 165 grams fat, 40 grams carbohydrates, and 75 grams protein.

“To be in a state of ketosis, it’s going to vary from person to person,” says Susie. “That might be 30 grams of carbohydrates for me, it might be 40 grams of carbohydrates for you, it might be 50 grams of carbohydrates for my sister. We’re all built differently.”

A low-carb, high-fat diet isn’t a good choice if you have pancreatic disease, liver conditions, gallbladder disease, or thyroid problems, and it can easily lead to constipation if you aren’t diligent with your fiber intake. Some studies show it can also increase your risk of heart disease.

Diets with fewer carbs and more protein typically bump your protein percentage up beyond the Centers for Disease Control and Prevention recommendation of 10%–30% of your daily calorie intake. The amount you aim for will depend on the plan you follow.

If you lean on red meats or full-fat dairy choices for your protein, you’re more likely to raise your risk of heart disease. When your body processes protein, it produces more metabolic waste, so if you deal with kidney issues, a low-carb, high protein diet could put a further strain on your system.

“It’s always a good idea to work with a registered dietitian to be sure that you’re not at risk for any potential vitamin or mineral deficiencies,” says Susie. “But overall I think that as long as you’re still consuming fresh fruits and fresh vegetables and legumes and not loading up your diet with overly processed foods because of a keto-friendly label, you’ll meet your needs.