Understanding the Science Behind What Does the Phrase We Are What We Eat Mean?

January 10, 2026 •

4 min read

French gastronome Anthelme Brillat-Savarin is famously credited with the sentiment 'Tell me what you eat and I shall tell you who you are' in 1826, laying the philosophical groundwork for the modern interpretation of the phrase we are what we eat. This idiom encapsulates a profound truth: our dietary choices are foundational to our overall well-being, influencing everything from our cellular health to our mental state.

Quick Summary

The saying 'we are what we eat' signifies that our diet critically influences our physical and mental health. It covers how food provides fuel, affects brain function, and shapes long-term wellness, extending beyond simple calorie intake to holistic well-being.

Key Points

Dietary Foundation: The food you consume provides the raw materials that build and maintain every part of your body, from cells to organs.
Mind-Body Link: The 'gut-brain axis' shows that diet profoundly affects mental health, mood, and cognitive function.
Energy Management: Nutritious foods offer stable, sustained energy, while processed foods lead to energy spikes and crashes.
Genetic Influence: Long-term eating patterns can influence genetic expression, affecting your risk of chronic disease over a lifetime.
Holistic Wellness: Beyond physical health, a good diet fosters positive mood, mental clarity, and overall well-being by nourishing the body and brain.
Origin Story: The phrase's roots trace back to 19th-century French and German philosophical thought and was popularized by an American nutritionist in the 1940s.

The Origins of a Timeless Adage

While the concept is ancient, the modern English phrase we are what we eat was popularized by American nutritionist Victor Lindlahr in the 1940s. His work emphasized the body's dependence on high-quality fuel, arguing that most diseases were caused by poor nutrition. However, the philosophical roots trace back further. Before Lindlahr, German philosopher Ludwig Andreas Feuerbach used the similar phrase "man is what he eats" in 1863, highlighting food's effect on one's mind and health. These early thinkers understood that diet was not merely about sustenance but was intricately linked to one's fundamental state of being.

The Physiological Truth: Food as Fuel and Building Blocks

The human body is a complex biological machine, and the raw materials it uses come directly from the food we consume. The quality, type, and quantity of these materials dictate how effectively the body can function, repair, and grow. This is why a diet of processed junk food leads to different outcomes than a diet rich in whole, nutrient-dense foods.

Consider the following functions:

Energy Production: Carbohydrates, proteins, and fats are the body's macronutrients, broken down to provide energy. A diet of simple sugars offers quick, but unsustainable energy, while complex carbs provide a steady fuel source.
Cellular Repair: Proteins, composed of amino acids, are the fundamental building blocks for repairing and maintaining tissues, muscles, and organs. Inadequate protein intake can impede this vital process.
Hormone Regulation: A balanced intake of healthy fats, such as omega-3 fatty acids from fish, is crucial for producing hormones that regulate mood, sleep, and appetite. Hormonal imbalances can arise from a poor-quality diet.
Micronutrient Supply: Vitamins and minerals, though needed in smaller amounts, are essential for countless bodily functions, from immune support to cognitive performance. Deficiencies can lead to physical and mental health problems.

The Gut-Brain Connection: A Two-Way Street

Beyond simple physical health, the phrase also points to the deep link between our diet and our mental state. The gut-brain axis is a well-established scientific concept that describes the communication network between your gastrointestinal tract and your brain. The bacteria in your gut microbiome play a crucial role in producing neurotransmitters like serotonin, which regulates mood.

Impact on Mood: A diet rich in fiber from plant-based foods nourishes the beneficial gut bacteria, leading to better neurotransmitter production and a more positive mood. Conversely, diets high in refined sugars and processed foods can cause inflammation, disrupting the gut-brain axis and increasing the risk of depression and anxiety.
Cognitive Function: Proper nutrition is vital for brain function. For example, omega-3 fatty acids are a key component of brain cell membranes and are linked to improved memory and reduced risk of dementia. Dehydration, a form of poor nutritional intake, can cause confusion and fatigue.

The Vicious Cycle of Poor Eating Habits

When we eat poorly, it can trigger a negative feedback loop. A greasy, high-sugar meal can lead to an energy crash and irritability. This can make us crave more unhealthy comfort foods, perpetuating a cycle of poor mood and poor dietary choices. Over time, this chronic inflammation and nutrient deprivation can contribute to serious long-term health issues.

The Holistic Impact of Dietary Choices

What you eat has consequences that extend to your long-term health and even your genetic expression. While a single unhealthy meal won't permanently alter your DNA, consistent dietary patterns over time can influence how your genes are expressed, potentially impacting chronic disease risk. This is particularly relevant in the field of nutritional psychiatry, which studies the role of diet in mental health. For example, the anti-inflammatory effects of a Mediterranean-style diet have been shown to improve symptoms in people with depression.

Diet Quality vs. Quantity Comparison


Feature	Nutrient-Dense Diet	Calorie-Dense, Processed Diet
Energy Levels	Sustained and balanced energy throughout the day due to steady glucose absorption.	Quick energy spikes followed by crashes, leading to fatigue and sluggishness.
Mental Acuity	Improved concentration, memory, and mood regulation due to essential nutrients and a healthy gut microbiome.	Impaired brain function, worsened mood, and increased risk of depression symptoms.
Cellular Health	Antioxidants and vitamins protect cells from oxidative stress and free radical damage, promoting longevity.	Promotes inflammation and oxidative stress, potentially damaging cells over time.
Long-Term Risk	Lowered risk of chronic diseases like heart disease, diabetes, and certain cancers.	Increased risk of chronic conditions such as obesity, heart disease, and Type 2 diabetes.

Conclusion

Ultimately, the phrase we are what we eat is far more than a simple health mantra; it is a scientifically grounded principle that underscores the profound, holistic connection between our food and our very being. From the energy that powers our every move to the delicate balance of chemicals that regulate our mood, our diet is the single most influential factor. By making conscious, nutritious food choices, we are investing in our immediate health, our long-term wellness, and our mental clarity. This shift from seeing food merely as fuel to a source of vitality and health is the true essence of the timeless phrase. For more information, consider exploring resources from the British Nutrition Foundation, which offers in-depth analysis on how food affects your brain and mood.

Frequently Asked Questions

The phrase's origins can be traced to 19th-century European philosophers, including Frenchman Anthelme Brillat-Savarin and German Ludwig Andreas Feuerbach. The specific wording was later popularized in English by American nutritionist Victor Lindlahr in the 1940s.

There is a strong scientific link between diet and mental health, often called the 'gut-brain axis.' The gut microbiome, influenced by what we eat, helps produce neurotransmitters like serotonin that regulate mood. A healthy diet supports a balanced microbiome, which in turn can positively impact mental well-being.

Yes, they absolutely can. Foods high in refined sugars and processed ingredients cause blood sugar spikes and crashes that lead to fatigue and low energy. In contrast, nutrient-dense, whole foods provide a steady release of energy, helping you maintain a consistent energy level throughout the day.

The gut microbiome is the collection of bacteria in your intestines. The food you eat directly influences the health and diversity of these bacteria. A healthy, diverse microbiome is crucial for digestion, nutrient absorption, and communication with the brain, all of which are essential for overall health.

Focus on incorporating more whole, unprocessed foods like fruits, vegetables, and whole grains into your diet. Make small, sustainable changes, such as swapping out sugary snacks for nuts or berries. Gradually reducing processed foods and increasing nutrient-rich options is key.

Research suggests that consistent dietary patterns can influence the expression of our genes over a lifetime, a field known as epigenetics. While you can't dramatically change your fundamental DNA, you can affect how your genes behave through nutrition, which can impact your long-term health.

Hydration is a core component of overall nutritional intake. The brain is primarily water, and even mild dehydration can negatively affect mental well-being, leading to anxiety, irritability, and poor memory. Staying properly hydrated with water is crucial for both physical and mental performance.