Humans are omnivores, meaning we are designed to eat both plants and animals. However, there is debate around what the ideal human diet should consist of. Proponents of plant-based diets argue that humans are evolutionarily adapted to eat mainly fruits, vegetables, nuts and seeds. Meanwhile, advocates of paleo and carnivore diets claim that humans thrive on meat and animal products. To understand what humans are truly meant to eat, we must examine our physiology and evolutionary history.
Human Physiology and Digestion
Humans have anatomical features reflecting our adaptation as omnivores. Our teeth include incisors for biting into fruits, vegetables and meats; canines for tearing meat; and molars for grinding plant foods. Salivary amylase helps break down starch from grains and vegetables. The human stomach produces hydrochloric acid to digest protein. The small intestine also secretes enzymes to break down fats, proteins and carbohydrates. Clearly, human digestion reflects an ability to effectively metabolize diverse foods, including both plant and animal sources.
However, some argue that while humans can digest meat, we aren’t well optimized for it. For instance, carnivores such as lions have a much shorter intestinal tract to quickly expel rotting meat. Omnivores like bears and dogs have powerful jaws to crush bones and consume organs. By comparison, humans have weaker jaws and longer intestinal tracts more suited to a diet rich in plant foods.
Nutrient Requirements
Looking at human nutritional requirements also provides clues into what we are designed to eat. There are certain nutrients that humans must obtain from dietary sources for optimal health. These include:
- Protein – Needed for building and repairing tissues. Found in both plant and animal foods.
- Essential fatty acids – Omega-3 and omega-6 fats. Found in plant oils, nuts/seeds and fatty fish.
- Vitamin C – Needed for immunity and collagen synthesis. Found in fruits and vegetables.
- Vitamin B12 – Needed for red blood cell formation and nerve function. Mainly found in animal foods.
- Iron – Needed for oxygen transport in blood. Found in both plant and animal foods.
This suggests that a variety of food groups containing both plants and animals are needed to meet human nutritional requirements.
Evolutionary Dietary Adaptations
Examining the diets of our early human ancestors gives insight into what we are genetically adapted to eat after millions of years of evolution.
Fossil evidence indicates our earliest human ancestors from 2-5 million years ago were opportunistic omnivores. They consumed insects, eggs, and small vertebrates, along with fruits, leaves, nuts and seeds. Stone tools to butcher meat first appeared 2.6 million years ago. This shows early humans were eating meat at least this far back.
Around 1.5 million years ago, major shifts in anatomy and behavior indicate adaptations toward increased meat consumption. Evidence shows regular scavenging of bone marrow and brains, indicating a higher quality diet. Changes in digestive anatomy (smaller teeth and jaws, larger small intestine) also show adaptation to a more readily digestible diet rich in animal fats and proteins.
By 50,000 years ago when modern humans emerged, isotope studies show meat and marine foods were a major part of hunter-gatherer diets. Our brains rapidly expanded over the past 250,000 years, providing further indication of high quality diets.
In summary, evolutionary evidence indicates humans are well adapted to make use of both animal and plant food sources thanks to our flexible omnivorous digestion.
Ancestral vs Modern Diets
Proponents of “ancestral” diets like paleo argue we should eat in line with our Paleolithic hunter-gatherer ancestors. This diet emphasizes meat, fish, eggs, vegetables, fruits, nuts and seeds, while excluding grains, dairy, legumes, processed foods and sugar.
However, critics argue our modern food environment differs greatly from ancestral conditions. Paleolithic humans ate wild game and plants, which had much higher nutrient levels than today’s domesticated meat and produce. Meat was consumed opportunistically in smaller quantities. Today’s grain-fed livestock, cultivated fruits/vegetables and highly processed foods are very different than anything in ancestral diets.
Additionally, genetics has continued shaping our digestion and metabolism since Paleolithic times. Populations like the Masai in Africa and Inuit in North America adapted to thrive on diets very high in animal foods. Some experts argue humans should customize diets according to more recent genetic ancestry, rather than try to mimic a one-size-fits-all Stone Age diet.
Ideally Balanced Omnivore Diets
Based on human anatomy, physiology and evolution, most experts conclude we are adapted for versatility as omnivores. However, opinions differ on what constitutes the ideal balance of plant vs animal foods. Here are some considerations for constructing an optimally balanced omnivore diet:
- Focus on whole, minimally processed foods – Plants like fruits, vegetables, tubers, whole grains, nuts and seeds; and quality sources of animal protein and fat like eggs, fish, poultry and lean red meat.
- Eat plenty of produce for essential vitamins, minerals, fiber – At least 400g or 5 servings per day.
- Include omega-3 rich foods – Quality animal proteins, fatty fish, flaxseeds, walnuts.
- Don’t overdo grains, especially refined grains.
- Limit sugars, especially from sugary drinks and processed foods.
- Stay adequately hydrated by drinking water.
- Customize based on needs and activity levels – Athletes may benefit from more carbs and protein.
- Maximize nutrient density to vitamin/mineral requirements.
Within these guidelines, some may thrive with a more plant-based diet while others do better with more animal foods. Paying attention to health markers and how you feel can help determine your ideal balance of plants and animals.
Typical Components of Balanced Omnivore Diets
Here are typical food group recommendations for a balanced omnivore diet meeting all nutrient needs:
| Food Group | Recommended Intake |
|---|---|
| Vegetables | 2-3 cups per day |
| Fruits | 1.5-2 cups per day |
| Whole grains | 3-5 ounces per day |
| Nuts/seeds | 1 ounce per day |
| Legumes | 1/2-1 cup a few times per week |
| Lean meats/poultry | 3-5 ounces 1-2 times per day |
| Fish/seafood | 8 ounces 1-2 times per week |
| Eggs | 1 per day |
| Low-fat dairy | 2-3 cups per day |
Within these recommendations, some populations like vegetarians can meet needs through plant sources alone. However, most people appear to optimize their health and longevity by including at least modest amounts of quality animal foods like fish, eggs, yogurt and cheese in an overall whole foods diet.
Key Points and Conclusion
In summary, extensive evidence indicates humans are adaptable omnivores designed to thrive on a variety of both plant and animal foods:
- Human anatomy and physiology reflect adaptations for effectively digesting and metabolizing diverse plant and animal sources.
- Both plants and animals provide optimal nutrient balance for human health.
- Evolutionary evidence shows early human diets were omnivorous and remained so up until modern times.
- Ancestral diets were highly variable based on food availability and genetic adaptations.
- Modern science supports balanced omnivore diets with plenty of minimally processed plants and moderate high-quality animal foods.
Rather than take an extremist approach, most people will optimize health by experimenting with their personal balance of plants and animals. Those thriving on vegetarian or vegan diets can continue this way. For others including some animal foods improves how they look and feel. The key is focusing on whole, nutrient-dense foods while meeting individual needs.