Nutrition & Supplements Complete Guide -- What, How Much, and Why to Eat

Introduction

We eat every day, yet surprisingly few people truly understand what and why they should eat. The internet overflows with contradictory nutrition information, and supplement ads make it seem like one pill can solve everything.

This guide systematically covers nutrition basics to supplement selection, age-specific recommendations, and common myths, all grounded in scientific evidence. If you want to build healthy eating habits, read through to the end.

1. Nutrition Basics -- Macronutrients and Calories

What Are Calories?

A calorie (kcal) is a unit of energy in food. Our body uses energy to breathe, maintain body temperature, and move muscles. When calorie intake exceeds expenditure, weight increases; when it is less, weight decreases. This is the fundamental principle of energy balance.

Carbohydrates

• 4kcal per gram
• The brain's sole energy source (glucose)
• Divided into complex carbs (brown rice, sweet potato, whole wheat) and simple carbs (sugar, white rice)
• Recommended ratio: 45-65% of total calories
• Dietary fiber: 25-30g daily recommended

Good carbohydrate sources: Brown rice, oatmeal, sweet potatoes, whole wheat bread, quinoa, fruits

Protein

• 4kcal per gram
• Building blocks for muscles, enzymes, hormones, and antibodies
• 9 essential amino acids must be obtained from food
• Recommended: 0.8-1.2g per kg body weight (athletes: 1.6-2.2g)
• Distributing 20-40g per meal is effective

Good protein sources: Chicken breast, eggs, tofu, salmon, Greek yogurt, legumes

Fat

• 9kcal per gram (highest caloric density)
• Essential for cell membranes, hormone synthesis, and fat-soluble vitamin absorption
• Unsaturated fats (olive oil, nuts, fish) are healthier
• Trans fats should be completely avoided
• Recommended ratio: 20-35% of total calories

2. Vitamins -- Types and Roles

Vitamins are organic substances that must be obtained from food because the body either cannot synthesize them or produces insufficient amounts. Water-soluble vitamins (B group, C) are not stored in the body and require daily intake, while fat-soluble vitamins (A, D, E, K) have better absorption when consumed with fat.

Vitamin Tips

• Vitamin D: Over 80% of people are deficient. Consider supplements especially during low-sunlight winters
• Vitamin C: Water-soluble; excess is excreted in urine. 500-1000mg daily is sufficient
• B vitamins: B12 supplementation is especially important during high stress or with vegetarian diets
• Vitamin A: Fat-soluble, so watch for excessive intake. Beta-carotene form is safer

3. Mineral Guide

Minerals are inorganic substances involved in bone, teeth, blood, and enzyme functions. They are divided into macro minerals (calcium, magnesium) and trace minerals (zinc, selenium).

Absorption Enhancing and Inhibiting Combinations

Good combinations:

• Calcium + Vitamin D = Increased calcium absorption
• Iron + Vitamin C = 2-3x increase in non-heme iron absorption
• Zinc + Animal protein = Improved absorption

Bad combinations:

• Calcium + Iron = Mutual absorption interference (take at different times)
• Zinc + Copper = Excessive zinc causes copper deficiency
• Calcium + Coffee/Carbonated drinks = Promotes calcium excretion

4. How to Choose Supplements

Priority vs Optional

No supplement is necessary for everyone. But given modern lifestyles, certain nutrients tend to be insufficient.

High priority supplements:

1. Vitamin D -- Most people are deficient. 1000-2000IU daily recommended
2. Omega-3 -- Consider supplementation if not eating fatty fish 2+ times per week
3. Magnesium -- Take before bed if experiencing stress or sleep issues

Situational additions:

• Vegetarians: B12, iron, zinc
• Pregnant/nursing: Folate, iron, DHA
• Middle-aged+: Calcium, Vitamin K2, CoQ10
• Athletes: Creatine, protein supplements, BCAA

Optimal Timing for Supplements

5. Age/Gender/Situation-Specific Recommendations

By Age

20s: Vitamin D (1000-2000IU), B-complex, Omega-3, Magnesium

30s: Above + CoQ10, Vitamin C, Probiotics, Zinc

40s+: Calcium + Vitamin K2 (bone health), Omega-3 (cardiovascular), Lutein + Zeaxanthin (eye health), Glucosamine/MSM (joints)

By Gender

Men: Zinc (testosterone synthesis), Selenium (sperm health), Saw Palmetto (prostate after 40s), Magnesium

Women: Iron (menstrual loss compensation), Folate (essential for women of childbearing age), Calcium + Vitamin D (post-menopausal osteoporosis prevention), GLA (PMS relief)

By Situation

Active exercisers: Protein supplements, BCAA/EAA, Creatine monohydrate (3-5g/day), Electrolytes

Students/Knowledge workers: Omega-3 (DHA), B vitamins, Magnesium, Lutein

Office workers (sedentary): Vitamin D, Omega-3, Probiotics, Magnesium

6. Gut Health and Probiotics

Why the Gut Matters

The gut is not just a digestive organ. About 70% of all immune cells reside in the gut, and over 90% of serotonin (the happiness hormone) is produced there. The balance of the gut microbiome significantly impacts immunity, mental health, and weight management.

The Gut-Brain Axis

The gut and brain communicate bidirectionally through the vagus nerve. This is called the "gut-brain axis" and is one of the most actively researched areas today.

Practical tip: Include fermented foods (kimchi, miso, yogurt, kombucha) in your daily diet and reduce processed foods and artificial sweeteners as a first step toward gut health.

7. Water and Hydration

How Much Water Should You Drink Daily?

The common "8 glasses (2 liters)" varies by person.

General recommendations:

• Adult males: About 3.7 liters (including food)
• Adult females: About 2.7 liters (including food)
• Pure beverages: Males about 3 liters, females about 2.2 liters

The Importance of Electrolytes

Water alone is not enough. Electrolytes (sodium, potassium, magnesium) must be adequate for water to be properly absorbed into cells.

8. The Science of Dieting

TDEE (Total Daily Energy Expenditure)

The core of weight management is understanding TDEE.

TDEE components:

1. Basal Metabolic Rate (BMR) -- 60-70%: Minimum energy for life maintenance
2. Activity (NEAT + Exercise) -- 20-30%: Daily activity and exercise
3. Thermic Effect of Food (TEF) -- ~10%: Energy for digesting/absorbing food

Macro Ratio Guide

Weight loss goal: Calories: TDEE minus 300-500kcal. Carb:Protein:Fat = 40:30:30. Maintain protein at 1.6-2.0g per kg (prevent muscle loss).

Muscle gain goal: Calories: TDEE plus 200-300kcal. Carb:Protein:Fat = 50:25:25.

Weight maintenance: Calories equal to TDEE. Carb:Protein:Fat = 45-55:20-30:25-35.

Dieting Precautions

• Severe calorie restriction (below 1200kcal) lowers BMR and causes muscle loss
• Weight can fluctuate 1-2kg daily due to water, intestinal contents, and hormonal cycles
• Judge trends by weekly average weight
• Waist circumference, clothing fit, and body composition are more important indicators than scale numbers

9. Common Nutrition Myths

Myth 1: Detox juices remove toxins from the body

Fact: Your body already has powerful detoxification systems -- the liver and kidneys. There is no scientific evidence that detox juices specifically "remove toxins."

Myth 2: Gluten-free is healthier

Fact: This is only meaningful for people with celiac disease or gluten sensitivity. Average people who avoid gluten may miss fiber, B vitamins, and iron from whole grains.

Myth 3: Eating collagen goes directly to the skin

Fact: Ingested collagen is broken down into amino acids during digestion. These amino acids are not guaranteed to be resynthesized as skin collagen. Vitamin C, UV protection, and adequate sleep are more reliable for skin health.

Myth 4: Egg yolks are bad because of cholesterol

Fact: Dietary cholesterol's impact on blood cholesterol is smaller than previously thought. Multiple studies show healthy people can eat 1-3 eggs daily without issues. Egg yolks contain valuable nutrients like choline, vitamin D, and lutein.

Myth 5: Too much protein is bad for kidneys

Fact: There is no evidence that high-protein diets cause kidney damage in people with healthy kidneys. Only those with existing kidney disease need to restrict protein. Healthy adults can safely consume up to 1.6-2.2g per kg body weight.

Myth 6: Only organic is healthy

Fact: There is insufficient decisive evidence that organic foods are significantly more nutritious than conventional foods. Whether organic or not, eating enough vegetables and fruits is the most important thing.

10. Conclusion -- Food First, Supplements Second

Core Principles

1. Diverse natural foods are fundamental: Supplements are literally "supplements" -- they cannot replace meals
2. Fill only what is lacking: Identify actually deficient nutrients through blood tests
3. Watch for excess: Fat-soluble vitamins (A, D, E, K) and minerals carry toxicity risks when taken excessively
4. Combinations and timing matter: Distinguish what should and should not be taken together
5. Consistency is key: Do not give up after one month without results; observe for at least 3 months
6. Reduce processed foods: No supplement can offset a processed-food-heavy diet

Practical Checklist

• Include protein in every meal (palm-sized portion)
• Eat vegetables/fruits of 5 or more colors daily
• Drink 1.5-2+ liters of water daily
• Minimize processed foods and added sugars
• Take basic supplements (Vitamin D, Omega-3) consistently
• Check nutritional status with annual blood tests
• Maintain adequate sleep (7-9 hours) and regular exercise

Disclaimer: This article is for educational purposes and does not replace professional medical advice. Nutrient needs and amounts may vary depending on individual health conditions. Consult a doctor or nutritionist before starting supplements, especially if you have underlying conditions or are taking medications.