#291
Last post, I zoomed into one tiny vitamin (B12). This time, let’s zoom out to the big three: carbohydrates, protein, and fat. Think of your body as a little economy running on a daily calorie budget. Carbs and protein bring in 4 calories per gram. Fat brings in 9, giving the body more than twice the energy for the same amount in weight.
Carbs: Cash on Hand
Carbs are quick energy, ready to spend. Your brain is their biggest customer. It lacks the enzymes to burn fat for fuel, so it runs almost entirely on glucose.
Growing up in South India, rice was the staple and nobody called carbs evil. Then I moved to America, where carbs were public enemy number one. So I cut out rice, fruit, and most carbs for a couple of weeks. Result? Zero energy and plenty of fatigue. Lesson learnt. Carbs are not the enemy. The kind matters more. Complex carbohydrates like whole grains, lentils, and veggies keep the economy steady. Refined carbs like white bread and added sugar crash the market. Tip: The less processed a food is, the more efficiently the body can break it down into lasting energy.
Protein: Infrastructure
Protein builds and repairs everything. Muscle, enzymes, antibodies, even the net that clots a cut. No need to obsess over it, but when you train hard, your muscles put in a bigger order.
One lesson came up in both my nutrition course and my CrossFit certification: protein alone doesn’t build muscle. Muscle needs two signals. One is raw material, the amino acids from food. The other is demand. When you lift or push hard, your muscle fibers sense the strain and flip on a growth switch (called mTOR), which tells cells to start building. No workout, no switch. In one study, people on bed rest lost muscle at the same rate whether they ate extra protein or not.
So where does the extra go? The body has no warehouse for amino acids. The liver strips off their nitrogen and turns it into urea, which the kidneys flush out. The rest gets burned for energy or stored as fat. Which brings a caveat. More protein means more urea for the kidneys to filter. Research hasn’t shown clear harm to healthy kidneys, but for people with kidney disease, cutting back on protein may slow it down. More isn’t automatically better.
And if carbs run short, the body starts burning protein for fuel*. That’s like burning the furniture to heat the house. Plant-based folks can trade smartly too. Beans with rice, dal with roti. Together they cover what each one lacks alone.
*The full picture: when carbs run low, muscles and organs switch mostly to burning fat. The brain can’t use fat directly, so the body breaks down some protein, even from muscle, to make the glucose the brain needs. Stay very low-carb for a few days and the liver turns fat into ketones, which the brain can use for part of its fuel. That spares some protein, but the brain never fully quits glucose.
Fat: The Savings Account
Fat is the most energy-dense currency. It stores energy for later, helps make hormones, and lets you absorb vitamins A, D, E and K.
Back when fat became the bad guy, food manufacturers pulled it out of products and pumped in sugar and refined starch to keep the taste. Low-fat cookies, anyone? Sugar deserved the closer look all along.
Refined carbs and added sugars absorb quickly, so blood glucose spikes and the pancreas releases a surge of insulin. When glucose floods in faster than muscles can use it or store it as glycogen, the liver converts the surplus into triglycerides, a type of fat that circulates in the blood. High triglycerides are one of five markers of metabolic syndrome, along with a large waist, low HDL ("good") cholesterol, high blood pressure and high blood sugar. Three or more raise the risk of type 2 diabetes and heart disease. Sugar can still have a seat at the table, albeit a small one.
The Balance Sheet
My textbook recommends 45 to 65% of calories from carbs, 10 to 35% from protein and 20 to 35% from fat. CrossFit’s Zone diet keeps it tighter at 40% carbs, 30% protein and 30% fat. Zone runs a little lighter on carbs than the textbook. The rest comes down to bio-individuality, a fancy way of saying the same plate lands differently in different bodies. Genes, gut bacteria, activity level and food history all shape how each of us uses what we eat.
Somewhere back home, my mom’s plate of rice, dal and veggies is nodding along. She balanced this budget long before I learnt the math.