Metabolic Medical Newsletter #3 | September 2025 | The Case for Meat

After years of nutrition research that instilled fear and discouraged eating meat, I am pleased to see a move towards a more meat-friendly perspective.

We are the primates that left the trees two million years ago (Homo habilis) and began to eat meat. Initially, mostly as scavengers carrying stone tools, we nutritionally benefited from carcasses left by other predators. Our stomach acidity, one of the lowest pH levels among mammals, reflects one of our earliest adaptations. As our diet changed, our bodies evolved physically and biochemically to optimize a meat-based diet. Our small intestines lengthened to better absorb amino acids (proteins) and fatty acids from this nutrient-dense food. Conversely, our large intestines shortened as our diet contained less plant fibre: cellulose. For herbivores, like our primate relatives, a long colon allows their microbiome to ferment cellulose, converting it into short-chain fatty acids (acetate, butyrate, and propionate) needed for energy and fat storage. Why develop a long colon when you eat a diet rich in saturated fats? Our femurs lengthened to enable us to be excellent distance runners, tiring prey for the kill. Our arms shortened, as they were no longer needed for swinging through trees, but our shoulder joints became inherently unstable: all the better to throw a spear. Most importantly, our brains expanded with these heavy protein and fat-rich meals. As Homo sapiens for the past 250,000 years, we are not the biggest, fastest, or fiercest predators. However, our large brains and ability to work together through language, strategy, and tools have driven the extinction of megafauna (and many other animal species!), making us the deadliest predators on the planet. (Harari, 2015).

All these physical adaptations worked well with the biochemical changes that helped ensure our survival during times of famine. We developed a “survival switch”(Johnson, 2022) that takes fructose from honey and autumn fruit, converting it efficiently into fat in our liver. This reserve fuel would support us during periods of near-starvation over lean winter months. Although glucose is one of our fuel sources, our body evolved under stringent operational conditions. More than four grams of glucose dissolved in our entire five-litre blood volume will trigger our pancreas to release insulin, which moves glucose into muscles or stores it as glycogen. Any "leftover” glucose from a meal is converted into fat by insulin for leaner times. 

This remarkable ability to convert carbohydrates into fat helped our species survive severe adversity. Without this biochemical process, managed by insulin, we would have become extinct long ago. As a species, we should always be thankful.

But this “magic” has become maladaptive in our modern world. Our ancient biochemistry was no match for a century of ultra-processed food, seed oils, refined carbohydrates, and sugar at every meal. We are no longer fighting famine and starvation; instead, we are battling chronic disease and obesity. Over time, society increased the availability of convenience foods with lower prices (thank you, government subsidies), easier access through fast food restaurants, and grocery stores mainly stocked with fake food. In the 21st century, diseases typically associated with adults now affect children, including fatty liver and type II diabetes. How did this happen?

Our food guides began in the early 1980s and were created with good intentions, but with limited scientific evidence. In this large social experiment, fat was mistakenly identified as the main cause of diseases, especially heart disease and stroke. As we reduced fat in foods, inexpensive, abundant, and dopamine-stimulating sugar was added as a substitute. The harmful consequences became evident soon after. By 1988, Dr. Gerald Revan described “Syndrome X,” a new set of signs and symptoms later known as “Metabolic Syndrome” or insulin resistance. Paradoxically, obesity—the very issue the food guide aimed to address—rapidly worsened. The obesity rate, which was around 10% in the late 1970s, skyrocketed to over 40% within a generation. The pandemic has caused this figure to rise even further.

Figure 1 Prevalence of overweight, obesity, and severe obesity among adults aged 20 and over: United States, 1960–1962 through 2017–2018. From NCHS Health E-Stats (Fryar, Carroll, & Afful, 2020). Copyright 2020 by the National Center for Health Statistics.

So, what can we do? We can recognize that food guides are just that—guides, not rules. The people who created them were imperfect humans doing their best with the knowledge they had. However, there is also corporate influence involved, with food and drug companies making profits and biasing decision-makers.

After decades of fear-mongering nutrition research that discouraged humans from eating meat, I welcome the shift towards a more meat-friendly narrative. In a study from McMaster University published in Applied Physiology, Nutrition and Metabolism, Stuart Phillips et al. (2025) examined animal and plant protein intake and all-cause mortality, including cardiovascular and cancer deaths. Neither protein source was linked to all-cause or cardiovascular mortality. Unlike plant protein, animal protein was associated with a DECREASE in cancer mortality. How refreshing!

Many are surprised to learn that no study has established a causal connection between saturated fat and heart disease. I encourage you to explore the work of Dr. Zoe Harcombe, a researcher with a PhD in public health and nutrition (Harcombe, n.d.). Dr. Harcombe’s research has examined studies from the past 60 years trying to find a link between saturated fat or cholesterol and heart disease, but without success. A decade ago, even the American Heart Association removed its warning about cholesterol: “cholesterol is no longer a nutrient of concern.” 

I hope you choose to eat foods that help keep your insulin levels low, focusing on protein and fats to nourish and energize your body. Remember: we have essential fats and amino acids (protein), but no essential carbohydrates. Our ancient biochemistry knows how to thrive without them in our diet.

References

Fryar, C. D., Carroll, M. D., & Afful, J. (2020). Prevalence of overweight, obesity, and severe obesity among adults aged 20 and over: United States, 1960–1962 through 2017–2018. NCHS Health E-Stats. https://www.cdc.gov/nchs/data/hestat/obesity-adult-17-18/overweight-obesity-adults.htm

Harcombe, Z. (n.d.). Zoe Harcombe. https://www.zoeharcombe.com/

Harari, Y. N. (2015). Sapiens: A brief history of humankind. HarperCollins Publishers.

Johnson, R. J. (2022). Nature wants us to be fat: The surprising science behind why we gain weight and how we can prevent—and reverse—it. BenBella Books, Inc.

Papanikolaou, Y., Phillips, S. M., & Fulgoni, V. L., III. (2025). Animal and plant protein usual intakes are not adversely associated with all-cause, cardiovascular disease–, or cancer-related mortality risk: An NHANES III analysis. Applied Physiology, Nutrition and Metabolism, 50(1), 1–8. https://doi.org/10.1139/apnm-2023-0594