Low-carb diets promise leaner bodies and better health. For many, they seem to work like magic. Some experts and influencers even claim that the era of “calories in, calories out” is over and that one can eat unlimited fat on a keto diet and still lose weight. Really? The truth is, whether measured in calories, joules, or even watts, every nutrient ingested carries reductive power derived originally from plants. This is settled biology, not slogans.
As a physical therapist, one of the reasons I love my trade is that we hardly depend on lab values, and we are certainly not armed with prescription pads. To restore function and improve the quality of life of our patients, we are teachers by necessity. It can rightly be said that physical therapists are the chief explainers in healthcare delivery. It is not easy to ask any human to do anything, therefore, every intervention must be explained to gain a patient’s confidence and compliance. Since becoming deeply interested in metabolic health through the physical therapy lens, I have noted blind spots and huge gaps in metabolic advice and even outright deception on social media. Patients and even professionals often misunderstand metabolism at its core. This is why sugar, the bedrock of all nutrients, has become the most hated molecule in pop culture.
Sugar, specifically glucose, is life’s first fuel. Every plant turns sunlight into glucose through photosynthesis, and every animal, including us, depends on that stored energy to move, grow, and think. Glucose is the molecule of construction, the brick and the energy that builds bone, muscle, and milk. In puberty, pregnancy, and breastfeeding, it is indispensable. During these phases, sugar’s job is creation, not destruction.
Unlike fruits and honey, breast milk is perhaps the only natural liquid sugar without any fiber, and no one in the ketogenic or low-carb community dares to call it dangerous. Why? Because sugar, when serving its contextual purpose, is the most powerful anabolic molecule on the planet. When infants are most sedentary in the early weeks of life, there is no such thing as insulin resistance or high blood glucose because sugar builds in context. I was reminded of this truth when I became a grandfather three months ago.
The fact is that no one looks at a growing baby and thinks “low carb.” We instinctively understand that infants thrive on anabolic nutrients, and at the center of it all is glucose, the primary skeleton from which fats and amino acids are made. Even bacteria can survive on glucose alone, building DNA and thousands of macromolecules. In the newborn, sugar is not indulgence but instruction to grow, divide, and develop. Red blood cells and parts of the kidney rely exclusively on glucose burning, and when someone is crashing with hypoglycemia or severe illness, nobody reaches for “keto-trose.” We give intravenous dextrose, another name for free glucose, because it is the body’s universal emergency currency, even in crisis.
However, in adulthood, when the body’s building projects are finished, sugar can become a liability. What once built life now feeds excess as free glucose floods the bloodstream through constant eating, sweetened drinks, and processed foods. The body’s growth machinery is compelled to stay switched on when it should rest, as nutrients are directed into storage even when there is nothing left to build and not much to burn. That is why low-carb diets seem to work: they pull back the flood through carbohydrate restriction. When glucose intake falls, insulin drops, and the body flips from construction to burning mode. It is not metabolic magic; it is chemistry finding equilibrium.
Fatty acids and ketones, the alternative fuels of low-carb metabolism, are primarily oxidative. They feed the body’s powerhouse to make ATP, and unlike glucose, fatty acids and ketones rarely build—they burn using inhaled oxygen. In stark contrast to sugar-derived amino acids, fatty acids and thousands of macromolecules, low-carb diets have limited building capacity, serving mainly to turn excess carbon into stored fat and cholesterol.
Each year, the Low-Carb USA community gathers to present data on weight loss and metabolic improvements, highlighting the effects of carbohydrate restriction on health. The numbers are often real, and people do lose weight and improve blood sugar control. But the interpretation turns those findings into dogma. They celebrate the outcome and miss the lesson. The real teachable moment is not that carbohydrates are evil, but that sugar’s chemistry is universal. It is an ubiquitous anabolic nutrient that sustains all life, yet it can cause metabolic disease and ill health in adults and even growing kids when consumed chronically and excessively. Context matters in biology.
Low-carb’s success is not about defying biology; it is about restoring rhythm. It mimics what used to happen naturally when food was seasonal and movement was constant. The body shifts between building and burning, growth and repair, feast and rest. When sugar intake stays high and motion stays low, that rhythm disappears, and with it, health nosedives. The lesson is not to fear glucose but to remember its context. Sugar was never meant to be a daily flood. It was designed to appear with purpose and vanish with use. Movement, fasting, and time were nature’s regulators long before diet books appeared.
Low-carb works because it unintentionally reminds the body of its original design: to build when needed and to burn when done. The challenge is not to live without sugar, but to live with rhythm—to let glucose flow with physical exertion and fasting, not stagnate as it does in the modern sedentary world filled with cheap sugar delights.
Mukaila Kareem, a doctor of physiotherapy and physical activity advocate, writes from the USA and can be reached via makkareem5@gmail.com
