The honest truth about these trendy diets

This time of year, the subject of dieting is very popular with the promise of quick weight loss, but it's important to carefully choose your weight-loss strategy. Doing so can help you can drop unwanted pounds safely and successfully — and boost your performance. The below info was provided by Ms. Carolyn Zisman, a nutritionist working at the Human Performance Resource Center.

Low-carb diets

Diets that are typically very low in carbs (less than five percent of calories or 50 grams daily) and high in fat (70–80 percent) can put you into ketosis. This means your body is producing ketones, which uses stored fat (instead of carbs) for energy. Aside from glucose from carbs, ketones from fat are the only fuel your brain can use. You might lose more weight on a moderate-protein, high-fat diet than a typical low-fat one.

(U.S. Navy photo by Mass Communication Specialist 1st Class Todd A. Schaffer)

Additionally, you can lower some risks for heart disease and type two diabetes. These diets also eliminate sugars and sweeteners, and they help you increase your intake of vegetables, omega three-rich seafood, nuts, and seeds. However, keto-type diets eliminate all grains, pastas, breads, beans, starchy vegetables, and nearly all fruit, which are critical sources of fiber, vitamins, and minerals. Carb restriction also might lead to underfueling, hunger, fatigue, depression, irritability, constipation, headaches, and "brain fog," which can affect your performance. Ketosis might make it harder to meet the extreme physical and mental challenges of your duties, too.

Keto-type diets are also tough to maintain because there are carbs in nearly all foods, including fruits, vegetables, legumes (beans, lentils, and peanuts), dairy products, and grains. Since your body needs to sustain ketosis for weight loss, it might be especially hard in environments with limited food options.

“Caveman” diets

High-protein, moderate-fat diets focus on foods that your hunter-gatherer ancestors ate, including fruits, vegetables, lean meats, fish, nuts and seeds. They're also high in fiber and low in sodium and refined sugars. In addition, they're generally healthy and not too hard to follow — whether you're at home, the mess hall, or eating out.

Since these diets rely heavily on fresh food, it sometimes can take longer to plan meals. Fish and grass-fed meat can be expensive, too. Caveman-type diets also exclude entire food groups—such as whole grains, dairy, and legumes—and increase your risk for nutrient deficiencies. Also, there's no difference in a high-protein, low-carb diet vs. a reduced-calorie diet for weight loss.

Vietnamese chefs teach Sailors assigned to the aircraft carrier USS Carl Vinson (CVN 70) how to prepare local dishes.

(U.S. Navy photo by Mass Communication Specialist 2nd Class Tom Tonthat)

Carbs are your body's preferred fuel source, and limiting them can lower your performance. While a low-carb diet is easier to do because you can eat carb-rich, starchy vegetables such as potatoes or squash, there might be times when this isn't practical, especially if you're on a mission with MREs or limited produce.

Intermittent fasting

Intermittent fasting (IF) essentially involves skipping meals for partial or full days (12–24 hours), severely restricting calories for several days in a row, or eating under 500 calories on two non-consecutive days.

While some research from animal studies shows that restricted eating might benefit longevity, there's no evidence that it affects longevity in humans. However, those diagnosed with type two diabetes might be able to manage their blood sugar with IF. Fasting also can be effective with an average weight loss of 7–11 pounds over 10 weeks.

Still, IF can be hard for someone who needs to eat every few hours to sustain energy for physical and mental performance. Some will overeat on non-fasting days, so IF isn't recommended for those with disordered eating or type one diabetes — or if you take medications that require food.

Weight loss comes down to energy balance: Eat less or move more to burn extra calories. In terms of performance, you need to eat more often to ensure you're always sufficiently fueled, so fasting can be a challenge.

Cleansing or detoxification

"Detox" diets — also called "cleanses" or "flushes" — claim to help remove toxins from your body, leading to weight loss. Cleanses includes diets, supplements, drinks, laxatives, enemas, or a combination of these strategies.

Non-laxative cleanses or juice fasts can jump-start quick weight loss, but you still need to follow up with a proper approach that is realistic and sustainable. Since your calorie intake is very low on these particular days, it also can affect your physical performance.

Fort Monroe's Staff Sgt. Joshua Spiess prepares a head of garlic while competing for the Armed Forces Chef of the Year.

(U.S. Army photo)

Detox-related weight loss is often only temporary and likely results from water loss. You also might gain weight when you resume normal eating. Extreme low-calorie diets can lower your body's basal metabolic rate (the number of calories needed to perform basic, life-sustaining functions) as it struggles to preserve energy. Detox diets, which often require some fasting and severely limit protein, also can cause fatigue. They can result in vitamin, mineral, and other essential nutrient deficiencies in the long term, too. And the jury's still out on whether detox diets actually remove toxins from your body. Depending on the ingredients used, detox diets also can cause cramping, bloating, diarrhea, nausea, vomiting, and dehydration, so they aren't recommended for healthy and safe weight loss.

What’s the best way to lose weight and keep it off?

Quick weight loss (more than two pounds per week) can backfire in terms of health and weight maintenance. If you eat too little, your body might use muscle for fuel, instead of carbs (primary fuel) or fat (secondary fuel). Muscle burns more calories than stored fat, so losing muscle can actually slow your metabolism and ultimately make it harder to lose weight and keep it off.

The best approach is one that provides enough fuel — fruit, vegetables, whole grains, low-fat dairy, lean meat, fish, eggs, nuts, and healthy fats — to perform your duties and preserve muscle. Read HPRC's "Warfighter Nutrition Guide" for tips to maintain your overall health and body weight.

For safe weight loss, make sure you are not causing harm and still have enough physical and mental strength to perform well. Work with your healthcare provider or a registered dietitian to create a healthy eating plan. You also want to make lifestyle changes that include exercise, so you can stay in warrior-athlete shape.