Put two people on a diet and they will never (let’s repeat that: never) have the exact same results.
“The more we learn about nutrition, the more we see the need for personalized nutrition, and finding the right diet for the right person,” explains Donald K. Layman, Ph.D., professor emeritus of food science and human nutrition at the University of Illinois. “One diet might be really good for one person, but really bad for someone else.”
And that’s especially true when it comes to men and women. The two sexes respond to diets quite differently—and understandably so, considering the differences in our bodies, namely in our hormones. (Read about how and why men and women experience weight loss differently here.)
This certainly applies to trendy nutrition protocols, like Paleo, intermittent fasting, and keto. We asked the experts how each might affect men and women differently, to push you one step closer to finding the diet that works for your body.
The Ketogenic Diet
The purpose of a ketogenic diet is to force the body to run on fat, rather than carbs, for energy. How do you do this? By getting about 80 percent of your daily calories from fat. You’ll eat a moderate amount of protein, but limit carbs as much as possible—about 20 grams a day, which is less than you’ll find in a banana. Eating this way shifts your body into a state of ketosis, in which the body breaks fat down into ketone bodies, a sort of stand-in for carbs.
It can take anywhere from weeks to months to shift into ketosis and burn fat for fuel, and you’ll need to test your urine or blood to know for sure. Once the body makes the shift, though, increases in satiety hormones and fat metabolism may contribute to weight loss, according to a review published in the International Journal of Environmental Research and Public Health.
As you can imagine, this diet is hard for anyone to follow long-term, though men may have better luck. According to Layman, research has shown that a diet’s carb content is a large predictor of whether or not women will stick with it, he says. The more carbs women are allowed, the more sustainable the diet—as any gal who’s scarfed down half a pizza after going low-carb can tell you.
However, there may be worthwhile benefits for women struggling with hormonal issues, namely polycystic ovarian syndrome (PCOS), which is often marked by insulin resistance and can lead to a snowball weight gain, infertility, and diabetes. In one study of obese women with PCOS, following a ketogenic diet for 24 weeks led to significant improvement in both weight and fasting insulin levels. “Because PCOS is driven by an imbalance of estrogen and progesterone, and higher insulin levels, a lower carbohydrate diet may help to create a more insulin-sensitive environment and allow the body to use fats and proteins for fuel,” Smith-Ryan says.
According to the researchers, though, the results of this study were similar to those of previous studies in which women consumed up to 100 grams of carbohydrates per day, which qualifies as low-carb but not ketogenic—suggesting women with PCOS can improve their symptoms without having to cut fruit out of their lives. A low-carb—but not severely low-carb—diet is often recommended (and successful), says Layman.
By dividing days and weeks up into “fasting” and “feasting” periods, intermittent fasting protocols (which exist in a variety of forms, including high and low-calorie days or only eating during certain hours, like 12 to six P.M.), may promote weight loss by making it easier for some dieters to cut calories.
While more research is needed to know exactly how it works, studies suggest that there may be advantages to intermittent fasting beyond cutting calories, Layman says. For instance, a 2017 review from the National Institute on Aging notes that fasting triggers physiological stress pathways that enhance DNA repair and metabolic health. Additionally, a review out of Brazil notes that intermittent fasting can improve the blood lipid profile (lower triglyceride levels, specifically) and inflammatory responses of men.
It’s worth noting, though, that despite fasting’s potential health benefits, a 2017 JAMA Internal Medicine study concluded that it’s no better for weight loss than typical calorie-counting.
Though intermittent fasting can help some people lose weight, it’s not exactly easy to sustain. Case in point: A third of the participants in that JAMA Internal Medicine study we just mentioned dropped out.
And while throwing in the towel is an issue for both men and women, the psychology involved in fasting may pose a different, more serious threat to women. When it comes down to it, intermittent fasting is about “saving up” calories for later, a behavior that can lead to or worsen disordered eating. “Many women will penalize themselves so they can indulge later,” says Layman—a behavior that’s much less common in men. For that reason, he doesn’t recommend anyone—male or female—with a history of body image and eating disorders attempt intermittent fasting. Considering 20 million American women and 10 million men will deal with an eating disorder at some point in their life, fasting may not be a risk worth taking—especially for women.
Rich in meat, fish, fruits, vegetables, nuts, and seeds—and devoid of dairy, legumes, processed foods, and refined sugars—Paleo is all about eating as closely as possible to how our ancestors supposedly did. But because the diet doesn’t address calories or how much of each macronutrient (protein, fat, and carbs) you’re eating, the results are largely contingent on what you do eat while following the diet, Layman says. (Eating a Paleo diet that’s all fruit and nuts will affect your body differently than one full of lean protein and vegetables, for example.) However, Paleo does offer one big benefit: a diet free of refined and processed sugars.
“Fifty-five percent of Americans’ calories come from carbs and roughly 90 percent of the carb calories come from grains. So if you stop eating grains, you likely lose weight,” Layman says. And since most of the processed foods people eat—like crackers, pretzels, pasta, and mac and cheese—are made from refined grains, which offer little nutritional value, nixing processed foods may be a good idea.
For many people, the Paleo diet tends to be pretty meat-heavy, and that may make it more mouth-watering to men, Layman says. After all, data from the U.S. National Health and Nutrition Examination Survey shows that the average man eats significantly more meat, poultry, and fish than the average woman.
That said, Paleo can be successful for men and women alike, as long as you can maintain a balanced diet after eliminating dairy, legumes, salt, processed foods, and refined sugars. However, it’s important to make sure that you don’t miss out on the calcium and vitamin D that dairy supplies. This is especially big for women, who are at an increased risk of osteoporosis and tend to require higher intakes to keep their bones strong, according to the National Osteoporosis Foundation. (You can get calcium elsewhere, like in dark leafy greens or sardines. Vitamin D can also be found in mushrooms, especially those treated with UV lights.) Women should meet with their doctor or a dietitian to make sure their intake of these two nutrients is still adequate while following Paleo.