Why one person's meat can be another person's poison and how it informs nutrition coaching.

Ever notice how a dish that fuels your friend’s afternoon feels a little heavy on you? That little mismatch is more common than you’d think. The saying “One man’s meat is another man’s poison” isn’t a perfect proverb, but it nails a real idea: people respond to food in wildly different ways. And for anyone coaching others on how to eat well, that idea matters a lot.

What that phrase really means

To put it plainly: nutrition isn’t a one-size-fits-all deal. Some foods light up one person with sustained energy, while the same foods can leave another person feeling sluggish, bloated, or uncomfortable. The core message is variability—differences from person to person in how our bodies process foods, absorb nutrients, and respond to meals.

Let’s separate the drama from the data, though. Yes, dietary preferences shape what people actually eat and enjoy. But preferences are only part of the story. Food allergies and intolerances are another piece, and they’re important in their own right. Universal food effects? Not really. A single food can be wonderful for many, risky for others, and neutral for a few. The big takeaway: you can’t assume everyone will react the same way to the same plate.

Why this matters for anyone guiding others on eating well

If you’re helping someone build a nutrition plan, recognizing variability changes everything. A plan that works beautifully for one person might cause problems for someone else. The dangers of ignoring this are real: missed cues of intolerance, lingering energy slumps, or simply meals that feel unsustainable because they don’t fit a person’s daily rhythm.

Think about it this way: you’re not designing a rigid menu; you’re crafting a flexible map. The best routes accommodate how a person actually feels, moves, and routines. That requires listening—careful observation, honest feedback, and a willingness to adjust. It’s a collaborative process more than a prescription.

The biology behind why people differ

Here’s the short version of the science behind variability:

• Metabolism and enzymes: People have different enzyme activity that helps break down carbs, fats, and proteins. Even small shifts can change how quickly energy appears after a meal.

• Genetics: Your genes can influence taste sensitivity, appetite signals, and how your body handles certain macro and micronutrients.

• Microbiome: The gut’s trillions of microbes can alter fermentation, gas production, and how you extract energy from foods.

• Health status and life stage: Hormonal changes, illnesses, medications, age, and pregnancy all tilt how you respond to the same foods.

• Lifestyle and context: Sleep, stress, activity, and meal timing can amplify or mute a food’s effects.

That’s a lot of moving pieces, and no single person carries every factor in one neat box. The point for coaching is not to map every detail but to recognize where personalization matters most.

How to spot variability in real life

You don’t need fancy tests to tune into individual differences. Start with simple, practical observations:

• Energy patterns: Do some meals spark steady energy, while others trigger a dip?

• Digestive responses: Bloating, gas, heartburn, or stool changes can signal intolerance or sensitivity.

• Mood and focus: Are you sharper after a protein-rich meal or after a fiber-rich plate? Do certain foods affect sleep?

• Performance and recovery: How do meals align with workouts or daily activity? Are there meals that support recovery better than others?

• Reactions to common offenders: Some people tolerate dairy, gluten, or high-FODMAP foods with no issue; others notice a clear link to symptoms.

Assessment tools that help (without turning anyone into a lab rat)

• Food diary or app logs: A week of recording what you eat plus how you felt helps reveal patterns.

• 24-hour recall conversations: A guided chat about the previous day’s meals can uncover hidden issues.

• Dietary history: A broad look at past eating patterns, preferences, and cultural foods can prevent you from throwing away what actually works.

• Basic biomarkers: When appropriate and ordered by a clinician, labs like fasting glucose, lipid panels, or inflammatory markers can offer clues.

• Symptom checklists: Quick screens for common intolerances or sensitivities can flag areas to explore.

Practical coaching moves that respect variability

• Start with a flexible framework: Aim for balance, not perfection. A plate that includes a protein source, colorful vegetables, some healthy fats, and whole grains is a good baseline, but you tailor it to each person.

• Use modular plans: Create core components (protein targets, fiber goals, hydration) and swap in foods that fit a person’s tastes, budget, and culture.

• Emphasize listening over dictating: Invite feedback after meals. What felt good? What didn’t sit right? Let the data you collect guide adjustments.

• Tune portions gradually: Small tweaks beat big, abrupt changes. A modest increase in protein at lunch can shift fullness and energy without feeling overwhelming.

• Build in consistency with flexibility: A “most days” approach helps people stay steady while allowing for social meals, cravings, or travel.

• Respect intolerances and preferences: If dairy upsets someone, offer tasty non-dairy alternatives. If a person avoids gluten, focus on naturally gluten-free options that still deliver satisfaction.

• Prioritize nutrient density without dogma: It’s not about labeling foods as good or bad; it’s about ensuring nutrient needs are met in a way that feels sustainable.

Common pitfalls and how to sidestep them

• Assuming a single solution exists: If you chase one perfect plan for every person, you’ll miss the nuance. Meet people where they are and adjust as you learn.

• Overlooking non-food factors: Sleep, stress, and activity share the stage with meals. Ignoring these can obscure true food responses.

• Failing to check in regularly: Quick check-ins help catch drift early. If a plan isn’t working, the faster you adjust, the better the outcome.

• Relying on labels instead of experience: Food intolerances can be subtle. Don’t rely solely on a label; listen to the body’s signals.

• Underestimating the power of culture: Food is tied to memory, family, and identity. Plans that respect culture have better staying power.

Examples from everyday life

• A vegetarian athlete might thrive on legumes and grains, but some individuals tolerate them less well during intense training blocks. A simple swap—tuning meal timing or choosing easier-to-dare protein sources like eggs or dairy (or their alternatives)—can keep energy steady.

• Someone with irritable bowel tendencies may experience improvements with a higher-fiber approach that comes from a variety of vegetables and tolerated whole grains, while another person finds certain fibers trigger discomfort. A patient, iterative approach that tracks symptoms alongside intake will reveal the best path.

• A person with a sugar sensitivity might respond differently to sweet-tavored meals. Replacing refined sugar with naturally sweet sources like fruit or dairy can smooth energy fluctuations, while still giving room for treats in a balanced way.

When to seek a specialist’s eye

Most variability can be managed with thoughtful coaching, but some signals warrant professional input:

• Persistent, unexplained symptoms after standard adjustments.

• Suspected allergies or celiac disease.

• Severe digestive issues, rapid weight changes, or suspicious lab results.

• Chronic conditions where nutrition interacts with medications (for example, diabetes or kidney disease).

A human-centered mindset for nutrition coaching

Here’s the throughline: you’re not just building meals; you’re shaping a relationship with food that fits a person’s life. The phrase about meat and poison serves as a helpful reminder: people’s bodies respond in their own ways, and your job is to learn those responses and adapt.

That means a coaching style that blends empathy with evidence. It means staying curious, inviting feedback, and ditching the urge to control every outcome. It also means celebrating small wins—the day a client notices steadier energy after a new lunch, or feels less bloated after a week of mindful adjustments.

Final thoughts: embracing the nuance

When you meet someone for a meal plan, you meet them with a question mark in your pocket. What works for you may not work for your neighbor, and that’s not a fail; it’s the nature of human biology. Your role as a nutrition guide is to help reveal what that individual response looks like and to map a path that feels doable and inviting.

If you keep that spirit—the humility to test, the flexibility to adapt, and the respect for personal variation—you’ll empower people to choose foods that nourish their bodies and support their everyday lives. And yes, you’ll also create a coaching experience that’s honest, sustainable, and genuinely human.

A quick recap

• The phrase points to individual variability in nutrition, not universal food effects.

• Personal differences come from biology, health, lifestyle, and culture.

• Start with a flexible framework, use practical assessments, and tailor plans to each person.

• Watch for red flags that call for professional input.

• The best nutrition coaching blends science with empathy, guiding people toward food choices that feel right for them.

If you’re crafting a plan for someone, think about what helps them feel strong, energized, and in control. Food should fit into life, not the other way around. And that mindset—curious, flexible, and human—will make the journey not only effective but also enjoyable.