The Obesity Epidemic: Fueled by the Standard American Diet
In the 1960s, America was lean: only about 13% of adults were obese, and roughly 45% were overweight or obese combined. Home-cooked meals and smaller portions were the norm. Many people smoked and few exercised. Dieting was common but obesity was not.
Then came the Standard American Diet — the SAD. High in sugars, refined carbs, and ultra-processed foods—the SAD is relentlessly improved each year to be tastier and cheaper. Any restaurant or store that wants Americans’ business must now compete at a very high level of satiety, deliciousness, and affordability.
The health picture has changed significantly. Now in 2025, 27 percent of U.S. adults are overweight, 39 percent are obese, and 9 percent are morbidly obese. And those numbers are rising — projections say 78 percent of Americans will be overweight or obese by 2030. The average American man, at 5’9”, has a BMI of 29 (200 lbs), while the average woman, at 5’4”, has a BMI of 28 (170 lbs).
Doctors aren’t immune — the 2007 Physicians Health Study reported that among 19,000 doctors, 40% were overweight (BMI 25–29.9) and 23% were obese (BMI ≥30).
This epidemic, costing $173 billion annually, is no longer just dietary or lifestyle-driven—it’s a spiral, with insulin resistance now the main driver. To understand the multiple causes, let’s look at the major factors driving obesity:
Insulin resistance
Dietary shifts
Price
Availability
Portion sizes
Sedentary lifestyles
Socioeconomic factors
Dietary belief systems that keep failing
Epigenetic factors
Let’s break these down.
Dietary shifts
In the 1960s, Americans ate home-cooked meals with whole foods—vegetables, lean meats, and minimal processing. In 2025, the SAD dominates, with 60% of calories from ultra-processed foods packed with added sugars (17% of daily intake, triple the recommended limit), and refined grains. Fast food and sugary drinks have replaced balanced meals, with lunch and dinner markets now dominated by fast-casual chains and drive-thrus offering high-calorie, low-satiety options. These foods, engineered for palatability and repeat business, drive overconsumption and fuel insulin resistance.
Insulin resistance
A minor factor in the 1960s, insulin resistance is now a central driver of the obesity epidemic. Diets high in refined sugars and carbohydrates cause repeated blood glucose spikes, desensitizing cells to insulin and promoting fat storage while increasing hunger. This spiral is worsened by pregnancy-related insulin resistance, which increases maternal weight gain and predisposes future children to obesity. The effect is nonlinear — once people get to a certain threshold, insulin resistance really kicks in and starts an ever-increasing spiral of weight gain and further progress toward diabetes, which has doubled since 1980. Insulin resistance, powered by highly processed foods, carbohydrate-rich products, and plenty of sugar in almost everything, is now the number one public health threat for Americans. It’s reversible simply by doing the opposite of what it took to get it — a low-carb diet, fewer calories, and plenty of exercise. Italians, who love their pastas and desserts, limit their portion sizes, get protein in every meal, and are far more physically active than Americans are.
Price
The cost of food has shifted dramatically since the 1960s, when whole foods were relatively affordable. Thanks to aggressive lobbying, agricultural subsidies for corn, soy, and sugar have made processed, calorie-dense foods like sugary snacks and fast food cheaper than fresh produce, whose prices have risen faster. A fast-food meal costs around $5, while a healthy meal with vegetables and protein can exceed $15. This price disparity pushes low-income households toward the SAD, exacerbating obesity rates and insulin resistance, as affordable foods are often the least satiating and most calorie-dense.
Availability
In the 1960s, grocery stores and home cooking were the norm. By 2025, food deserts — areas with limited access to fresh foods — plague low-income urban and rural communities, forcing reliance on convenience stores and fast-food outlets stocked with SAD staples. Fast-casual chains and vending machines are ubiquitous, offering quick, cheap, high-carb options. This lack of access to nutrient-dense foods, combined with the omnipresence of processed ones, drives overconsumption and perpetuates obesity, particularly in underserved populations. One consequence of highly available food is that people aren’t used to going hungry — a natural condition for 99 percent of human existence. People would be better off going hours at a time with a bit of hunger. While multi-day fasts tend to destroy muscle in proportion to fat, limiting windows for eating during the day can be very beneficial. Instead, we are surrounded by cheap, tasty food all day long.
Portion sizes
Portion sizes have ballooned since the 1960s, when a soda was 12 ounces and a burger 4 ounces. By 2025, fast-food meals routinely include 32-ounce drinks and 8–12-ounce burgers, often exceeding 1,000 calories. Restaurants and packaged foods have followed suit, with oversized servings marketed as value. All-you-can-eat restaurants are popular and encourage overeating. These larger portions, often low in satiety due to refined carbs, directly contribute to weight gain and insulin resistance.
Sedentary lifestyles
The 1960s featured active daily routines—manual jobs, walking, and chores. By 2025, Americans average 8+ hours of sitting daily, tied to desks, screens, and cars. Urban design discourages walking, and children prioritize gaming over outdoor play. This shift, entrenched since the 2000s, reduces movement and worsens insulin resistance, as inactive muscles become less responsive to insulin, promoting fat storage and amplifying the effects of calorie-dense diets.
Socioeconomic factors
In the 1960s, obesity was less stratified by income. Today, low-income adults face a 46 percent obesity rate compared to 34 percent for college graduates. Limited income, long work hours, and lower nutrition literacy drive reliance on cheap, calorie-dense SAD foods. Families don’t eat dinner together nearly as much as they did decades ago. Tasty deserts are common after both lunch and dinner.
Dietary belief systems and fads that keep failing
The 1980s–2000s low-fat craze, which vilified fats and promoted carb-heavy, low-satiety foods, misled consumers into overeating sugars and starches. Diet gurus like Dr Dean Ornish even used the president of the United States as a case study for a low-fat lifestyle, paving the way for more insulin resistance and weight gain. By 2025, despite the decline of low-fat dogma, new fads — extreme diets, detoxes, and processed “health” foods — persist, often backed by misleading marketing. These beliefs, rooted in oversimplified (or zero) science, fail to address satiety or insulin resistance, perpetuating poor dietary choices and obesity.
There’s no end to the number of bad — and popular — diet books on the market.
Epigenetic factors
Negligible in the 1960s, epigenetic changes are now a small but growing factor. By 2025, maternal obesity (over 25% of pregnant women) and insulin resistance alter fetal gene expression, increasing offspring’s obesity risk through mechanisms like DNA methylation. This generational effect, driven by the SAD and rising maternal health issues, compounds the epidemic, subtly amplifying vulnerability in a feedback loop with dietary and socioeconomic drivers.
Poor food choices at schools
The prevalence of poor dietary options in schools, often dominated by processed foods high in sugar, sodium, and unhealthy fats, has been a significant contributor to childhood obesity and related health issues. School lunches frequently include items like pizza and fries that are full of chemical additives. Nutrition experts like Dr. Mark Hyman and Dr. Marion Nestle have been vocal advocates for transforming school food systems to prioritize health. Hyman has pushed for initiatives like introducing salad bars, eliminating junk foods from menus, supporting farm-to-school programs, teaching cooking skills, and banning junk-food marketing targeting children. Nestle, a prominent nutritionist and food policy expert, has criticized the influence of the food industry on school meals, noting their high sodium and sugar content, and advocates for systemic changes such as stricter regulation of food additives and policies to promote healthier, less processed options. Their combined efforts emphasize the need for policy reforms and educational campaigns to foster healthier eating environments for students.
Summary
Americans are fatter than ever. Reversing this demands overhauling food systems, addressing inequities, and breaking the metabolic spiral. Mostly, it involves education and better availability of affordable, healthy foods. Don’t choose the default SAD, make better choices and transform yourself — become leaner, stronger, and help others get out of the dietary trap 70 percent of Americans find themselves in. This is a good video to continue your learning: