From Population Requirements to Personal Nutrition Calibration | Part III
Part 3 of the Series Introducing Nutrition from First Principles
Standing in your kitchen at 6 PM, staring into the refrigerator, paralyzed.
You know more about macros, inflammatory foods, cholesterol, carbs, and high fructose corn syrup than your grandparents ever even considered. You can recite the glycemic index of every item in your pantry. You know what the doctor said. But you still do not know what you should really eat for dinner.
The kale makes you feel virtuous and bloated. The sweet potato sends your energy crashing two hours later. The grass-fed beef fits your protocol but leaves you reaching for something you cannot name. Every choice carries the weight of optimization. Did you pick the most anti-inflammatory option? The most nutrient-dense? The one your latest lab results suggest?
Meanwhile, your body keeps sending signals you have learned to override. Cravings get dismissed as bad habits. Fatigue gets blamed on insufficient willpower. The conversation between what you know and what you feel grows louder until eating becomes a daily exercise in managing competing theories instead of nourishing an actual human system.
Here is what it looks like when you stop asking what is optimal and start asking what is real.
From Theory to Kitchen Counter
The constraints that govern human nutrition operate the same whether you are standing in that kitchen or reading research papers. The protein ceiling. The Randle cycle. The isotopic evidence from bones. The metabolic mechanisms we explored last time.
These constraints do not shift with dietary trends or expert disagreements. They simply are.
When you understand them, the paralysis in front of the refrigerator starts to dissolve. Not because you found the perfect diet, but because you can see which approaches respect metabolic reality and which create contradiction.
Guardrails and a Spectrum
When biochemical constraints, historical evidence, metabolic mechanisms, and individual verification converge, a clear pattern emerges from hard science. Not a prescription, but what the constraints permit and what they eliminate.
The constraints do not dictate a single diet. They create guardrails. Inside those guardrails is a spectrum of workable templates. Different diets land in different places on that spectrum, mostly based on which fuel dominates and how many variables your system has to juggle.
Step outside the guardrails long enough and the result is predictably ugly: metabolic dysfunction and a distortion of natural signals like hunger, energy, body comfort, and mental clarity.
Where you belong on the spectrum depends on your genetics (AMY1, lactase, APOE), your activity level, your current metabolic health, and what you can verify through direct experience.
So let’s look at common dietary patterns through the same lens. Let’s see how each one sits inside the guardrails, and which ones tend to run over them.
What the Constraints Reveal About Popular Diets
Ketogenic (70 to 75% fat, 20 to 25% protein, 5 to 10% carbs)
A ketogenic diet stays inside the guardrails when it respects the protein ceiling and commits to a single fuel mode. It pushes the body into fat oxidation and uses the ketogenic machinery humans clearly have. It also fits the broader historical picture of high animal intake for long stretches of time, especially when you remember the protein ceiling forces that animal intake to be fat-centric.
What this often feels like, once you are past the transition, is a calmer appetite and steadier energy. The mid-afternoon crash fades. Hunger becomes informational instead of urgent. Many people report mental clarity improving, not because keto is mystical, but because their fuel supply stops swinging.
The most common reason people think keto fails is simple: they eat too lean. They keep carbs low and fat low and then blame the template for the predictable result, which is fuel insufficiency. If you are running 5 to 10% carbs, fat has to carry the load. That is not ideology. That is mechanics.
Paleo (30 to 40% carbs, 30 to 40% fat, 20 to 30% protein)
Paleo can sit comfortably inside the guardrails when carbs come from whole foods, protein stays under the ceiling, and fat stays high enough for satiety and stable energy. The advantage is not the label. The advantage is usually that it removes refined grains, sugar, and industrial oils while keeping food recognizable.
When it works, it tends to feel like steadier energy without feeling restricted. For people who tolerate starch well, it can support training and daily life without the volatility that comes from refined versions of the same macro ratio.
Where paleo gets weird is when it becomes modern “lean and clean.” Chicken breast and sweet potato can look ancestral on Instagram while missing the ancestral fat backbone that the protein ceiling practically demands in high animal-food diets.
There is another honest complication here. The plants we eat today are not what our ancestors encountered. Modern produce has been selected for sweetness, size, and palatability. A wild carrot is thin and bitter. A wild banana is seed-heavy with little edible pulp. Even leafy greens have been shaped to reduce defensive compounds that made them harder to eat.
This does not invalidate vegetables. It just means the phrase “eat like our ancestors” is not literal. The label is a story. The guardrails are real.
Mediterranean (35 to 40% fat, 40 to 45% carbs, 15 to 20% protein)
The Mediterranean pattern often works when it is actually Mediterranean, meaning whole foods, meaningful fat intake from quality sources, and carbs that are not refined. It tends to sit inside the guardrails for people with decent carbohydrate tolerance and, in many cases, long agricultural ancestry that correlates with better starch handling.
When done well, it often feels stable and sustainable. Appetite stays reasonable. Energy stays steady. The combination of fat and whole-food carbs can be deeply satisfying without turning into constant hunger.
The failure mode is the common “Mediterranean” caricature: pasta, bread, low-fat sauces, and a marketing halo. The studied benefits came from diets built around fish, olive oil, nuts, vegetables, and minimally processed foods. Not restaurant bread baskets.
Carnivore (70 to 80% fat, 20 to 30% protein, 0 to 5% carbs)
Carnivore is the extreme end of the animal-food spectrum. It can sit inside the guardrails when it is fat-centric and respects the protein ceiling. It forces complete fuel commitment and strips variables to almost nothing, which is precisely why it can be useful.
For people with significant food reactivity or gut noise, the felt experience can be dramatic. Bloating can drop fast. Cravings often quiet down. Decision fatigue disappears. That simplicity is not a small thing. For some people, it is the first time in years their body feels readable again.
Where people get into trouble is the same place as keto: too lean, too fast, and not enough support during transition. Another issue is mistaking early relief for a finished answer. Sometimes carnivore is a long-term fit. Sometimes it is a powerful elimination phase that reveals what can be reintroduced later without losing the signal you just regained.
Vegan (10 to 15% fat, 10 to 15% protein, 70 to 80% carbs)
Vegan is the most difficult to reconcile with the deep-time isotopic baseline, and it typically runs closer to the guardrails for many people. It often requires supplementation (B12 at minimum, and commonly iron, zinc, and omega-3 support in some form). It also has to solve protein quality and adequacy without animal foods, which can be done, but it is not trivial.
It can still “work” for some people, especially when it replaces a standard Western diet. Getting out of engineered food alone can improve satiety, mood, and energy. Some people also report symptom relief when they remove animal foods, which may reflect quality issues with what they were eating (factory-farmed meat, conventional dairy, processed foods) rather than a universal rule about animal foods.
The felt experience is highly variable. Some people feel light and steady. Others feel persistently hungry, struggle to maintain muscle, and get energy swings that never fully settle.
One more complication that matters here, especially if we are being honest about “ancestral” framing. Modern plant foods are agricultural products bred for traits that did not exist in the wild at this scale, especially sweetness and starch density. A vegan diet built on modern sweet fruits, starchy vegetables, and processed grains is not simply “plant-based.” It is a very modern fuel environment. That does not make it impossible. It does mean the execution matters more, and verification matters more.
Standard American Diet (35% fat, 50% carbs, 15% protein)
This is the metabolic incoherence case study. It sits outside the guardrails because it combines refined carbs with added fats in a way that keeps insulin signaling fat storage while the diet supplies constant storage substrate. It also leans heavily on industrial oils and engineered foods designed to override satiety.
What this feels like is painfully familiar: constant hunger despite adequate calories, energy that peaks and crashes, cravings that feel neurological rather than nutritional, and a general sense of never being satisfied. Inflammation shows up as joint pain, brain fog, poor sleep, skin issues, or mood instability.
This is neither the fat-centric pattern suggested by the protein ceiling and deep-time evidence, nor the whole-food carb pattern some agricultural societies adapted to. It is a modern combination with no clean metabolic mode.
What This Reveals
The constraints do not dictate a single diet. They reveal the guardrails of what is mechanistically possible.
Fat-dominant approaches tend to work when protein stays moderate and carbs stay low enough to avoid mixed-fuel confusion.
Carb-moderate approaches tend to work when carbs are whole foods, fat stays adequate, and the diet does not drift into refined carbs plus added fats.
Carb-dominant approaches can be survivable and sometimes helpful, but they often require personal genetic adaptation and tighter attention to protein adequacy, essential nutrients, and food quality.
For the last fifty years, the carb-dominant approach has been considered the gold-standard by nutritional standards. The sight of the food pyramid was ever present in my primary and into post graduate class rooms. It is burned into my memory, solidified by blind faith in research experts and textbooks.
What does not work is the modern mixed pattern: high refined carbs plus high seed oils plus added fats plus inadequate protein. This violates metabolic coherence and has no stable historical precedent. The constraints eliminate it before any debate starts.
(To be fair, Moon Pies® and RC® cola didn’t fit into the U.S. Nutritional Guidelines either. The guidelines did, however, incentivise industrialized oils and margarine, refined grains and high-fructose corn syrup. In other words, it created inexpensive raw materials for the processed food industry. The Standard American Diet was destined to be highly accessible and very convenient.)
How to Locate Yourself on the Spectrum
This is not about choosing the morally superior diet. It is calibration within constraints.
Here is the loop:
Pick a starting point. Hold it steady long enough to get clean signal. Track boring signals. Adjust one lever at a time.
Pick a starting point
Choose a template that sits inside the guardrails and that you can actually follow without turning your life into a constant negotiation.
If your current diet is essentially the Standard American Diet, the first move is rarely macro optimization. It is removing engineered foods and refined inputs that override satiety and distort signals.
After that, you choose a fuel strategy to test.
Hold it steady long enough to tell the truth
Most people quit during the transition and call that a conclusion.
Expect the first week to be noisy if you change fuel strategies. Electrolytes shift. Appetite shifts. Gut motility shifts. Sleep can change. Mood can change.
Then, if you stay steady, the signal often clarifies across the next several weeks. A useful rule of thumb is 4 to 6 weeks for a meaningful read, especially when gut symptoms are part of the story.
Track boring signals
You do not need a spreadsheet to do this. You need honesty and consistency.
Pay attention to:
Energy stability across the day
Hunger and satiety clarity
Craving intensity and frequency
Sleep quality
Mood steadiness
Digestive comfort
Starches are a clean example of how this works. For some people, starch is fuel. For others, starch triggers bloat, fog, cravings, or an energy crash one to two hours later. That is not a character flaw. It is a calibration clue.
Adjust one lever at a time
Once you have a baseline, small changes teach you more than big swings.
Some of the highest leverage levers:
Carb level and carb source (starch versus fruit versus refined)
Dairy in or out
Fat quantity, especially on low-carb approaches
Fat type, if you suspect sensitivity
Plant reintroduction after elimination phases
Genetics can inform which lever to test first, without turning into destiny.
If you have high AMY1 from agricultural ancestry, you may tolerate whole-food carbs better, and your best-fit template may sit more toward the carb-moderate side. If you have lactase persistence, dairy may be available as a dense, stabilizing food, unless it creates consistent symptoms. If you carry APOE4, you may want to test fat sources more carefully and pay attention to lipid responses as part of your verification.
The key is that genetics suggests what to test, not what to obey.
Optional Tracking and Accelerants
Labs and tools can help, but they are optional.
They can reveal constraints you cannot feel yet. They can create motivation by making the invisible visible and reduce uncertainty when your internal signals are noisy.
They also have a failure mode: they can become a new way to outsource reality.
Use them with a purpose and a time horizon. Baseline, experiment, recheck.
More than one teaspoon of sugar in your blood is toxic. Yet a plain, medium baked potato converts to about 8 tsps of sugar.
The body must have tight regulations on glucose control.
Fasting glucose and HbA1c levels show if your diet is pushing your body out of its ability to maintain these tight controls.
Hs-CRP levels, has proven useful as it is a gross marker for inflammation. Use this marker when reliable sensitivity panels are unavailable.
Likely your physician will put emphasis associating higher LDL (the “bad” cholesterol) levels with cardiovascular disease, while emerging groups are countering the fifty year old narrative. Cholesterol (LDL levels) is a poster boy for the contradictory health attention economy. This is for another discussion.
If cholesterol is a concern, a lipid panel with particle size can add context, interpreted in the full metabolic picture, not as a standalone verdict.
A better alternative, in my opinion is the triglyceride to HDL ratio. your proper foods will keep that lower an elevated marker.
I often see few key types of functional labs help to reveal otherwise hidden blockers and are useful when natural signals are blunted (hunger, mental clarity, immune triggers).
Microbiome testing when gut symptoms dominate and you need directional insight
Food sensitivity testing when immune reactivity is obvious and early elimination decisions feel impossible
Continuous Glucose Monitors (CGMs) when glucose volatility is clearly part of the problem and you like to experiment with real-time food reactions
Again, optional. Helpful when used well. Not required to make progress.
Expect Transition Noise
Expect any significant dietary change to be bumpy at first.
The transition is often roughly a week of withdrawal-style disruption followed by several weeks of adaptation, especially in the gut. After just the first few days, natural hunger signals often start to return, while energy stability, digestion, and clarity recalibrate across the 4 to 6 week window.
A lot of kitchen paralysis is not ignorance. It is experimental chaos. Too many changes, too little time, and no clean signal.
From “Should” to “Can” to Clarity
The protein ceiling operates in every human liver. Energy density follows thermodynamics. Isotopic signatures cannot misreport. Metabolic cycles are observable in any laboratory.
These are not opinions. They are constraints.
Each constraint eliminates possibility spaces. The protein ceiling rules out lean-meat diets. Energy density explains fat prioritization. Isotopic evidence points to long stretches of predator-level intake. The Randle cycle shows why the modern high-carb plus high-fat pattern predictably breaks people. Genetic variation tells you where to test. Direct experience completes verification.
When these constraints converge, contradiction dissolves. Not because someone declared victory, but because reality leaves less room for fantasy.
This is what “can” reveals. Not what someone says you should do, but what the human body can actually tolerate, what the evidence suggests actually happened, what metabolic mechanisms can sustain, and what your own system confirms when you run a clean test.
Beyond Nutrition
The method applies beyond nutrition.
When examining gut dysbiosis, you do not just prescribe probiotics and hope. You look at what is mechanically blocking balance, then address those constraints.
When working with emotional processing, you do not need unverifiable explanations. You can use the direct felt experience of resistance dissolving as a form of verification, because it is observable without faith.
The same filters work whether you are interpreting a stool test or working through a repeating internal pattern. Start with constraints. Build from mechanisms that do not require belief. Verify through direct experience.
This creates a different kind of trust. Not trust in a practitioner’s authority or a dietary ideology, but trust in mechanisms that operate independently of belief. When something works, you can often see why. When something does not work, you have the literacy to adjust without abandoning the entire approach.
The point is not the diet. The point is replacing “should” with “can.” Nutritional confusion thrives when people are forced to live inside other people’s conclusions. Constraint-based reasoning starts from what cannot be otherwise, then trusts your system to reveal what works within those boundaries.
Nothing written here is meant to diagnose or treat. Educational purposes only.