Why Low-Carb Diets Lead to Quick But Not Lasting Weight Loss
By Marissa Hull, Registered Dietitian, and John Bulmer, Public Information Officer, Capital Cardiology Associates
March is National Nutrition Month, and there's no better time to take a closer look at the nutritional choices that shape your long-term health. This month, Capital Cardiology Associates is releasing a three-part series addressing some of the hottest nutrition topics on social media, separating the noise from the science. This is Part Two.
Following a low-carbohydrate diet, whether Keto, Atkins, or another variation, has been a popular weight-loss strategy for decades. Many people report real results, at least initially. But there is an important distinction that often gets lost in the enthusiasm: rapid weight loss is not the same as sustainable weight loss.
"I have heard many times in my career individuals tell me, 'the only way I have lost weight in the past is by cutting out carbs,'" says Marissa Hull, Registered Dietitian on the Cardiometabolic Clinical team at Capital Cardiology Associates. "However, they blame weight regain on themselves not being able to stick to the diet long-term, and not the diet itself."
Why the Scale Drops So Fast at First
When carbohydrates are drastically reduced, the body turns to its stored form of carbohydrates, called glycogen, for energy. Glycogen is held primarily in the liver and skeletal muscles. The critical detail is what happens when glycogen breaks down: for every gram of glycogen the body uses, approximately three grams of water are released along with it.
"This is why individuals lose weight rapidly in the beginning of dieting," Hull explains. "A lot of the weight that is lost is water being released when glycogen is broken down." The number on the scale falls quickly, but much of that initial loss is water, not body fat.
What Your Brain and Body Actually Need
Carbohydrates are not the enemy. They are the body's preferred source of energy. The brain alone requires roughly 120 grams of carbohydrates each day to function properly. When that supply is cut off, the consequences are noticeable: fatigue, irritability, and difficulty concentrating are common early symptoms of carbohydrate deprivation.
The Muscle Loss Problem
Beyond fatigue, carbohydrate restriction can quietly undermine something most people are trying to preserve: muscle. Carbohydrates work alongside protein to maintain and build muscle mass. Losing muscle is particularly damaging to long-term weight management because it slows the metabolism, setting the stage for plateaus or future weight regain.
"As a dietitian who has used body composition scales on my patients dieting and losing weight, I personally have seen individuals who strength train and consume 120 grams or more of protein daily and still lose muscle because they did not consume enough carbohydrates," Hull says.
Cravings and the Cycle of Regain
One of the more insidious effects of long-term carbohydrate restriction is what it does to cravings. The body continually signals that it needs carbohydrates to function, and the longer those signals go unmet, the stronger they become. The problem is that the body doesn't necessarily crave the healthiest sources. After prolonged deprivation, people tend to crave calorie-dense, nutrient-poor foods like cookies, candy, and desserts, not fruits, whole grains, or starchy vegetables.
The result is a predictable cycle: restrict carbohydrates, lose weight quickly, experience mounting cravings, eventually give in, and regain the weight, often more than was lost. Each time, the person blames their own willpower rather than recognizing that the diet itself was working against them.
What You Lose When You Cut Carbs Completely
Healthy carbohydrate foods, including fruits, starchy vegetables like potatoes and corn, and whole grains, are not simply vehicles for sugar. They deliver cholesterol-lowering fiber, cancer-preventing antioxidants, and a range of vitamins and minerals that support overall health. Eliminating them because they contain carbohydrates means losing all of those benefits along with them.
The good news is that fueling the body with adequate carbohydrates throughout the day actually reduces the intensity of cravings, which makes it easier, not harder, to maintain a healthy diet over time.
The Bottom Line
Low-carbohydrate diets can produce fast results, but the mechanisms driving those early results are largely water loss, not fat loss. The long-term consequences often include muscle breakdown, metabolic slowdown, and intensifying cravings that are difficult to ignore indefinitely. A sustainable approach to weight management doesn't require eliminating carbohydrates. It requires choosing the right ones, eating them consistently, and allowing the body to function as it was designed to.
Marissa Hull is a Registered Dietitian on the Cardiometabolic Clinical team at Capital Cardiology Associates, where she works with patients to improve their eating habits, make smarter nutritional choices, and manage their weight. For nutritional guidance or to schedule an appointment, visit capitalcardiology.com.
Medical Disclaimer
The information in this article is intended for general educational purposes only and does not constitute medical advice. It should not be used as a substitute for professional medical guidance, diagnosis, or treatment. Individual nutritional needs vary; please consult your physician or a qualified healthcare provider before making changes to your diet.
