The Unexpected Connections Shaping Our Health
Imagine a scene from 18,000 years ago in Maszycka Cave, Poland. A group of Magdalenian hunter-gatherers carefully processes human remains, making precise cuts to remove muscle tissue and breaking bones to access the nutritious marrow within3 . This archaeological evidence of cannibalism presents a stark contrast to today's global obesity epidemic, where the struggle is not with food scarcity but with abundance. What connects these seemingly unrelated phenomena?
The story of human body weight is more complex than simple calories in versus calories out.
It's a tale woven from threads of evolutionary biology, neuroscience, and modern food environments.
Recent scientific discoveries are revealing surprising insights about how our bodies manage energy, why obesity has become so widespread, and how our prehistoric past might hold clues to addressing this modern health crisis. From the cognitive impacts of obesity to the alarming rise in extreme weight categories, researchers are uncovering a story that challenges long-held assumptions about diet, exercise, and willpower.
For decades, the prevailing wisdom about obesity centered on an energy imbalance: we're eating too much and moving too little. The solution seemed straightforward—exercise more. But a groundbreaking study published in 2025 turns this assumption on its head.
When evolutionary biologist Herman Pontzer and his international team compared daily calorie burn across 34 different populations, they discovered that total daily calorie expenditure was remarkably similar across vastly different lifestyles1 .
"Our bodies tend to adjust how we expend energy to keep our total calorie burn stable within a pretty narrow range. If we burn more of our energy every day on physical activity, after a while our bodies will adjust and spend less energy on the other tasks that we don't notice going on in the background."
This finding suggests that the primary driver of the obesity epidemic isn't decreasing physical activity levels but changes in what we're eating. As Dr. Dariush Mozaffarian, director of the Food is Medicine Institute at Tufts University, starkly puts it: "It's 100% the diet"1 .
The critical shift in our food supply has been the rise of ultra-processed foods. In populations where these foods dominate, obesity rates are significantly higher1 . These engineered food products appear to disrupt our body's natural hunger and satisfaction signals, leading to overconsumption even when our energy needs have been met.
While diet plays the leading role in weight gain, scientists are discovering that obesity fundamentally changes our brains—and that these changes might be reversible. In an August 2025 study, French researchers made a breakthrough discovery about how obesity affects brain function.
The research focused on astrocytes—star-shaped brain cells in the striatum, a region involved in perceiving pleasure from food4 . Scientists found that high-fat diets and obesity reshape these previously overlooked cells, which play a crucial role in regulating both metabolism and cognitive abilities affected by obesity, such as learning and task flexibility4 .
Even more remarkable, when researchers manipulated these astrocytes in mice using chemogenetic techniques—essentially installing a molecular "switch" to control calcium flow in the cells—they could influence metabolism and restore cognitive functions impaired by obesity4 . This suggests that targeting these specific brain cells could open new avenues for obesity treatments that address both metabolic and cognitive aspects of the condition.
High-fat diets alter brain cell function, particularly astrocytes in the striatum4 .
Obesity impairs learning abilities and task flexibility through brain changes4 .
Manipulating astrocytes can restore cognitive functions affected by obesity4 .
While obesity rates across all categories have risen concerningly, the most dramatic increase has occurred in the most severe forms. Research from Pennington Biomedical Research Center reveals an alarming trend: while overall obesity rates in the United States increased by approximately 30% between 2004 and 2023, the rate of individuals with a body mass index of 60 kg/m² or greater increased by 210%.
To put this in perspective, while a person with a BMI of 30 might be 30-40 pounds overweight, someone with a BMI of 60 or greater is typically more than 200 pounds overweight. This extreme obesity category now includes an estimated 850,000 people in the U.S. alone.
This dramatic rise in extreme obesity presents serious challenges for healthcare systems, as these patients often exceed weight limits for standard medical equipment, complicating everything from biomedical imaging to anesthesia and surgeries.
| BMI Category | Percentage Increase | Estimated Population Affected |
|---|---|---|
| All obesity (BMI ≥30) | 29.5% | Not specified |
| Extreme obesity (BMI ≥60) | 210% | >850,000 people |
Returning to our prehistoric starting point, research into the nutritional aspects of cannibalism provides fascinating insights into the relative value of the human body as a food source. While this may seem macabre, understanding the calorie content of the human body helps archaeologists interpret whether prehistoric cannibalism was primarily driven by nutrition or ritual.
A 2017 study in Scientific Reports created the first comprehensive nutritional template for the human body, calculating that a typical adult male contains approximately 125,822 total calories6 . The distribution of these calories reveals which body parts would have been most sought after for nutritional purposes.
| Body Tissue | Mass (kg) | Caloric Value (kcal) |
|---|---|---|
| Skeletal muscle | 24.897 | 19,951 |
| Adipose tissue (fat) | 13.539 | 81,234 |
| Bone marrow | 2.576 | 12,096 |
| Liver | 1.565 | 2,009 |
| Blood | 5.043 | 4,481 |
| Skin | 3.183 | 6,051 |
| Other organs | 9.693 | Not specified |
When compared to other prey animals of similar size, humans have a comparable nutritional value, but significantly less than larger fauna like deer or bison that were often available to prehistoric groups6 . This suggests that when prehistoric humans practiced cannibalism, the motivations were likely more complex than simple nutrition—possibly involving social, cultural, or ritual elements.
Human body: ~125,822 total calories
Less nutritional value than larger prey animals like deer or bison
Modern obesity research employs sophisticated tools to unravel the complex biology of weight regulation. The study on astrocytes highlights several cutting-edge approaches:
Allows precise control of specific cell types (like astrocytes) using engineered proteins and activating compounds.
Visualizes structural and functional changes in brain regions affected by obesity.
Analyzes gene expression in individual cells to understand how they change with aging and obesity.
Quantifies how the body burns calories and utilizes energy at the whole-body level.
Assesses changes in learning, memory, and behavioral flexibility associated with obesity.
The interconnected tale of swarms (the complex systems governing our biology), cannibals (our evolutionary past), ageing (the cellular processes affected by obesity), and human obesity reveals a fundamental truth: body weight regulation is not a simple matter of willpower but a complex interplay of biology, environment, and evolution.
Diet quality, not just calorie quantity, drives obesity, with ultra-processed foods playing an outsized role1 .
Obesity fundamentally changes brain function, particularly in cells like astrocytes that influence both metabolism and cognition4 .
The most severe forms of obesity are rising at alarming rates, requiring new medical approaches and treatments.
As research continues, the focus is shifting from blaming individuals to understanding the biological systems that make weight management challenging for so many. The most promising developments recognize that obesity is not a personal failing but a complex medical condition influenced by our evolutionary history, modern food environment, and fundamental neurobiology.
The path forward will likely require solutions as multifaceted as the problem itself—from public policies that improve food environments to medical treatments that target the specific brain pathways disrupted in obesity. By learning from our past and present, we can develop more effective and compassionate approaches to this pressing health challenge.