Over the past two months, Prime Lab has been unpacking the three macronutrients — carbs, fats, and protein — from both a scientific and practical lens. After all, over a ton of food and water enters our bodies each year. What we choose to eat — or avoid — deserves some precision.
Our stance has been clear: quality comes first, then quantity.
Because if your daily intake is perfectly portioned out into grams of syrup protein bars and deep-fried trans fats like churros, then all that “precision” is just engineering a metabolic disaster with greater accuracy.
That said, quantity still matters. Caloric restriction (CR) has long been a poster child in longevity research. Numerous studies suggest that modest reductions in total calorie intake can improve biomarkers of healthy aging — and even extend lifespan in some animal models.
But let’s put that “geek-level longevity experiment” aside for a moment. Let’s go back to something more grounded:
How much should we actually eat each day?
And in what macronutrient proportions?
1. Resting Metabolic Rate: Your Body’s Idling Engine
Think of your body as an engine. Even when you do nothing at all — not scrolling your phone, not daydreaming — it still burns fuel just to keep you alive: heartbeat, breathing, temperature regulation, liver and kidney functions. This idle fuel burn is called your Resting Metabolic Rate (RMR).
The commonly used Mifflin–St Jeor equation estimates RMR based on your gender, age, height, and weight. For Asians, RMR tends to be 6–10% lower than for Western populations; I’ve applied a 7% correction factor in the following example 2,3.
Take me as an example: 42 years old, Asian male, 70 kg, 180 cm. My calculated RMR is roughly 1,507 kcal.
(10 × 70 kg + 6.25 × 180 cm − 5 × 42 + 5) × (1 − 7%) ≈ 1,507 kcal
You don’t need hyper-precision here — clinical metabolic cart tests might differ by 5–10%, which is acceptable for daily planning.
To estimate Total Daily Energy Expenditure (TDEE), multiply RMR by a physical activity factor (e.g., 1.375 for light activity), or use actual data from your smartwatch or fitness tracker.
In my case: 1507 × 1.375 ≈ 2072 kcal
So beyond RMR, I’m burning an extra 565 kcal a day — just from walking, typing, gym sessions, or heated debates over “how to manage your carb intake.”
Note: not all of those calories turn into heat. Some are structural costs — repairing muscle, building membranes, synthesizing hormones. Calories are bookkeeping units, not just fuel readings.
And yes, the weight-loss classic still holds:
Intake < Expenditure → Your body fills the gap using glycogen, fat, and a bit of protein.
But today we’re assuming stable body weight, and shifting focus to macronutrient distribution.
2. Setting Your Macronutrient Ratio: Start with Protein
Most people begin with a neat ratio: 50% carbs, 30% fat, 20% protein, then multiply it by their total calories.
It looks elegant, but it’s not the most scientific.
A better approach? Start with protein:
- Determine your daily protein need based on weight, age, and activity level.
- Convert grams to calories (1g protein = ~4 kcal), then deduct protein calories from your total.
- Split the rest between carbs and fat.
Why prioritize protein?
Because it’s the hard currency of tissue repair and muscle maintenance — non-negotiable if you want to stay strong. But too much can burden your metabolism, so it demands precision.
Current mainstream recommendations suggest the following [4–7]:
- General adults: 1.2–1.5 g/kg/day (with a minimum intake of 0.8 g/kg/day)
- During strength training: 1.5–2.0 g/kg/day
- Healthy older adults: 1.0–1.2 g/kg/day; Older adults with sarcopenia: 1.2–1.5 g/kg/day; Individuals at risk of severe malnutrition: up to 2.0 g/kg/day
- Chronic kidney disease (non-dialysis): 0.55–0.8 g/kg/day (must be individualized and managed under medical supervision)
For me:
1.5 × 70 = 105g protein ≈ 420 kcal
That’s exactly 20% of my 2072 kcal daily budget.
Which leads to the real question:
How should I allocate the remaining 1650 kcal (≈ 80%) between carbs and fats?
3. Carbs vs. Fats: A Budget Tug-of-War
If you flip through the official dietary guidelines from various countries, you’ll find a strikingly consistent formula:
High carbohydrate intake: 45–65%
Moderate to low fat intake: 20–35%
Protein: fills in the remainder
With additional limits such as:
Free sugars < 10%
Saturated fat < 10% [8–10]
It sounds like a universally endorsed formula. But this is actually a public health safety net, not an optimal longevity blueprint for Prime Lifer.
Why do official guidelines lean high-carb, low-fat?
First, these recommendations are grounded in large-scale observational data and practicality.
The U.S. Dietary Guidelines for 2020–2025, for example, are built on massive datasets like NHANES, which contains hundreds of thousands of dietary records. China’s dietary recommendations are similarly informed by epidemiological surveys. But here’s the catch: in these real-world datasets, the quantity of carbs or fats is almost never separated cleanly from their quality.
In other words, the “high-carb” group often ends up being the high–added sugar, high–refined grains group. The “high-fat” group? Frequently loaded with saturated fat, red meat, and omega-6-heavy vegetable oils.
So, the conclusions drawn from these populations carry built-in context：
- Carbs are recommended in large proportions because, in reality, it’s hard to get the average person to completely give up sugar, cakes, and milk tea. (The WHO suggests keeping free sugar under 10% — we’d argue it should be closer to 0.)
- Fat is kept low because, frankly, most people’s fat sources are garbage — think fried chicken, fatty cuts of meat, and hydrogenated vegetable oils.
In other words, this is a defensive dietary model designed for a world where perfect food quality is hard to guarantee. It’s not the optimal longevity blueprint — it’s a public health safety net strategy: minimize risk, maximize scalability.
There’s also the factor of cost and feasibility. Staple carbs are cheap, easy to store, and universally accessible. Extra virgin olive oil and wild-caught salmon? Not exactly practical on a global scale. The WHO has to consider food supply chains and economic feasibility when setting global guidelines.
Put simply:
Public health guidelines are about keeping you out of the ditch — not teaching you how to fly.
4. Prime Lifers need First Principles Thinking
Now, if you’re someone who already has high-quality nutrition dialed in — your carbs come from low-GI, fiber-rich whole grains, legumes, fruits, and vegetables; your fats are from olive oil, nuts, and fatty fish; and your saturated fat is kept below 5–6% — then congratulations: you don’t need to be boxed in by the high-carb, low-fat model.
Why? Because in the scientific literature, studies that isolate and compare high-quality fats versus high-quality carbohydrates — after removing the confounding effects of poor-quality nutrients — are exceedingly rare. Without many direct answers, Prime Lifers have to turn to first principles and break the problem down from the ground up:
① Carbohydrates are essential —
Your brain and red blood cells depend on them (excluding ketones), so you can’t go zero-carb.
② But carbs typically result in higher blood glucose levels —
Even low-GI choices, when the glycemic load is high, can challenge glycemic and insulin control.
③ High-quality fats offer “gentle” energy —
They don’t spike glucose or insulin, instead, they promote fat oxidation, and when paired with aerobic exercise, can more effectively enhance mitochondrial metabolism. They’re calorie-dense, slow-digesting, and highly satiating — potentially helping reduce overall intake.
④ Both camps bring key allies —
Carbs carry fiber, polyphenols, and other protective compounds; fats bring Omega-3 and monounsaturated fats. Both are non-negotiable in a well-designed diet [11–14].
So, could we reasonably hypothesize that — assuming adequate protein — a slightly higher fat-to-carb ratio might be beneficial? Say, 40–45% fat and 35–40% carbs?
Actually, yes. And we have solid data to back it up.
In the landmark PREDIMED randomized controlled trial (Spain, n = 7,447, follow-up = 4.8 years), the Mediterranean diet group consumed around 41% of their calories from fat (about 9% from saturated fat). The result? A roughly 30% reduction in major cardiovascular events. In other words, high-quality fats at this level are not only safe in the real world — they may be protective [15–16].
So why not go full keto?
A fair question. Ketogenic diets (70–80% fat, ultra-low carb) come with plenty of short-term hype: stable blood glucose, lower triglycerides, rapid early weight loss (thanks to liver glycogen depletion and water loss).
But from a long-term health perspective, the jury’s still out — and the risks are worth unpacking [17–19]:
- Cholesterol spikes
High saturated fat + ultra-low carb can cause dramatic increases in LDL-C and ApoB in some individuals, which raises a clear atherosclerosis concern, especially for lean or normal-weight people.
- Nutrient gaps
Cutting out whole grains, legumes, and fruit also means missing out on “invisible armor” such as fiber and polyphenols.
- Underwhelming exercise performance
Fat is a less efficient fuel than carbs for endurance training. In plain English: you run slower, fatigue faster.
- Real-world compliance issues
Theoretically, keto is avocado, almonds, and salmon. In practice? It often devolves into butter, bacon, and seared red meat — risk profile goes up fast.
- Long-term sustainability is tough
Social settings, convenience, and taste preferences make strict keto hard to stick with.
A 4-week crossover RCT in young, normal-weight women found that a ketogenic diet (4% carb, 77% fat, 19% protein) increased every single participant’s LDL-C by an average of 1.82 mmol/L, with ApoB up 0.5 g/L.
A 2024 meta-analysis in AJCN also reported that lean or normal-weight individuals are more likely to see LDL-C spikes on low-carb diets. The same doesn’t necessarily apply to those with obesity or insulin resistance 20,21.
Prime Lab’s stance is clear: keto may be a powerful clinical tool for specific conditions, but it’s not designed to be a lifelong operating system.
5. Prime Lab’s Real-World Formula
For healthy adults, when protein is sufficient and both carb and fat sources are high-quality, it’s totally reasonable to skew slightly in favor of fat — without going to extremes.
Here’s my personal formula:
Carbs: 35–40%
Fats: 40–45%
Protein: 20%
Paired with regular lipid monitoring to ensure that LDL-C and ApoB don’t sneak upward with higher fat intake.
🏆 Benchmarking against the longevity elite
Take Bryan Johnson — the high-profile biohacker who spends millions optimizing his body like a Formula 1 machine. His daily menu looks like this 22:
- Calories: 2,250 kcal (he practices ~10% caloric restriction; adjusted to baseline, that’s ~2,500 kcal)
- Carbs: 35%
- Fats: 40%
- Protein: 25% (≈1.8 g/kg)
His protein is higher, for good reason — he’s older (48), trains hard, and needs to protect muscle mass under caloric restriction.
But his carb-to-fat ratio aligns closely with Prime Lab’s recommended longevity zone: slightly more fat than carbs, but nowhere like keto. Even among hardcore anti-aging enthusiasts, extreme high-fat/low-carb paradigms aren’t the go-to.
There’s also strong overlap in how macronutrient ratios are designed and prioritized.
One last reminder: Quality first, always
All discussions about quantities and ratios rest on the assumption that nutritional quality is already high：
- Carbs: No free sugars, low GI/GL, whole foods, whole fruits, and ≥30g of fiber per day
- Fats: No trans fats, saturated fat capped at 5–6% (as per AHA guidelines for LDL-C/ApoB reduction), balanced omega-6 to omega-3 ratio
- Protein: Primarily plant-based, with whey protein as a post-resistance training supplement
In nutrition, any discussion of quantity without a foundation of quality is a case of putting the cart before the horse.
In Summary
Public health guidelines are the safety net — a floor to keep the majority from getting it too wrong.
The Prime Lab method aims higher: it’s about optimizing risk-reward balance on top of high nutritional quality.
Here’re the simple steps:
- Start by setting a sufficient protein target based on your metabolic needs.
- Then divide the remaining calories between high-quality fats and high-quality carbs — with a slight tilt toward fats.
Remember: longevity isn’t about extremes. It’s about quality, balance, and sustainability.
Intervention recommendations are geared toward generally healthy individuals. If you have existing health conditions, always follow your doctor’s instructions.
References22
[1]AI Research
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[4]WHO/FAO/UNU.Protein and Amino Acid Requirements in Human Nutrition. WHO Technical Report Series 935, 2007.
[5]Morton, R. W., et al. “A Systematic Review, Meta-Analysis and Meta-Regression of the Effect of Protein Supplementation on Resistance Training–Induced Gains…” British Journal of Sports Medicine, 2018
[6]Bauer, J., et al. “Evidence-Based Recommendations for Optimal Dietary Protein Intake in Older People: PROT-AGE Study Group.” Journal of the American Medical Directors Association, 2013.
[7]Ikizler, T. A., et al. “KDOQI Clinical Practice Guideline for Nutrition in CKD: 2020 Update.” American Journal of Kidney Diseases, 2020.
[8]Chinese Nutrition Society & National Health Authorities. Explanation and Public Education on Macronutrient Energy Distribution Ratios (2022–2025). China, 2022.
[9]U.S. Department of Agriculture and U.S. Department of Health and Human Services. Dietary Guidelines for Americans, 2020–2025. 9th ed., 2020.
[10]World Health Organization. “Healthy Diet: Key Facts.” 2024–2025 online update.
[11]Gardner, C. D., et al. “Effect of Low-Fat vs Low-Carbohydrate Diet on 12-Month Weight Loss in Overweight Adults (DIETFITS).” JAMA, vol. 319, no. 7, 2018, pp. 667–679.
[12]Institute of Medicine. Dietary Reference Intakes for Energy, Carbohydrate, Fiber… National Academies Press, 2005.
[13]Augustin, L. S. A., et al. “Glycemic Index, Glycemic Load and Glycemic Response: An International Scientific Consensus Statement.” The American Journal of Clinical Nutrition, 2015.
[14]Vessby, B., et al. “Substituting Dietary Saturated for Monounsaturated Fat Impairs Insulin Sensitivity (KANWU Study).” Diabetologia, 2001.
[15]Estruch, R., et al. “Primary Prevention of Cardiovascular Disease with a Mediterranean Diet (Reanalysis).” The New England Journal of Medicine, 2018.
[16]Estruch, R., et al. “Effect of a High-Fat Mediterranean Diet on Bodyweight and Waist Circumference.” The Lancet Diabetes & Endocrinology, 2016.
[17]Iatan, Iulia et al. “Association of a Low-Carbohydrate High-Fat Diet With Plasma Lipid Levels and Cardiovascular Risk.”JACC. Advances vol. 3,6 100924. 25 Mar. 2024,
[18]Burke, L. M., et al. “Low-Carbohydrate, High-Fat Diet Impairs Exercise Economy and Negates Performance Improvements in Elite Race Walkers.” Cell Metabolism, 2017.
[19]Storz, M. A. “Nutrient Intake in Low-Carbohydrate Diets vs the DGA 2020–2025.” Proceedings of the Nutrition Society, 2022.
[20]Burén, J., et al. “A Ketogenic Low-Carbohydrate High-Fat Diet Increases LDL Cholesterol in Healthy, Young, Normal-Weight Women: A Randomized Controlled Feeding Trial.” Nutrients, vol. 13, no. 3, 2021, Article 814.
[21]Davis, A. V., et al. “Low-Carbohydrate Diets and Blood Lipids: A Systematic Review and Meta-Analysis.” The American Journal of Clinical Nutrition, vol. 119, no. 5, 2024, pp. 889–905.
