- Being overweight and obese are multifactorial conditions with important psychosocial and environmental contributors.
- Food processing, poor sleep, social facilitation, convenience, and distracted eating each measurably increase our calorie intake.
- Clinical trials and laboratory studies have helped us quantify exactly how much these factors increase eating.
What causes obesity? Why are obesity rates recently surging among populations of nearly every industrialized country? And what, if anything, can we do about it?
These were among the questions that led some of the field's top scientific minds to assemble Avengers-style at the prestigious Royal Society meeting in London last October. Their task was formidable: Solve the obesity pandemic, which the World Health Organization (WHO) argues is the largest public health threat facing humanity in the 21st century.
What causes obesity?
Soaring in prevalence here and abroad, obesity and being overweight contribute directly to each of the top 10 causes of death in the U.S., including deaths from heart disease and many forms of cancers but also deaths from infectious diseases and even accidents. These weight conditions have risen so dramatically in recent years, even among U.S. children and adolescents, that major medical bodies now recommend the use of weight-loss medicines and bariatric surgeries for people as young as 12 or 13 years old (according to the January 2023 clinical guidelines report published by the American Academy of Pediatrics).1 What insights could the Royal Society panel offer in the face of this metabolic doomsday scenario?
Debated and discussed over three vigorous days of scientific dialogue, society members concluded that the question about the cause of overweight and obesity has an answer but no convenient solution.
The scientific explanation for the raging pandemic is "energy balance." Or, to be more precise, "energy imbalance." Energy balance is the star of the infamous "energy balance equation," the latter being the technical description of what those of us not invited to Royal Society meetings might call "calories in, calories out." This ratio refers to the degree to which our energy intake (calories in) from food and beverages matches our energy output (calories out) in the form of resting metabolic activities, exercise, and the many other energy-intensive functions of your mercurial body.
The energy balance equation premise is simple: Consume too many calories on a regular basis, and some of this energy becomes stored as body fat. As body fat accumulates–especially if the fat builds up in the abdominal area where it is called visceral fat–it begins compromising metabolic health. In practice, compromised metabolic health means that organs, tissues, and cells can't use or produce energy effectively.
Because you are essentially an energy factory that happens to walk and talk, the inability to make or use energy effectively has serious consequences. Imagine your car sputtering down the road because it can no longer use gasoline efficiently or your house lights flickering on and off because they can't utilize electrical energy properly. That's the same kind of effect that occurs in the body of an energy-dependent human.
The classic signs of impaired metabolic health are metabolic diseases. Common metabolic diseases such as prediabetes, hypertension, and hyperlipidemia are really "shots off the bow," early warning signs of a malfunctioning metabolic system. Unmanaged or unrecognized, they eventually spiral into the "most wanted list" of metabolic diseases, such as cardiovascular diseases, diabetes, cancer, and dementia.
Why are we overeating?
Remarkably, the above metabolic domino effect results from a pattern of simply eating too much. Too much sugar? Steak? Vegetables? Studies indicate that the energy source matters less than the total energy consumed; excess energy from any food source acts as a slow toxin to our metabolic system ("energy toxicity" is the hip term for energy imbalance on social media these days).
The question even the Royal Society conference members didn't answer was, "Why are we overeating?" Overweight and obesity, after all, were rare in all parts of the world until a few decades ago, but human genetics are unchanged, and we possess no less self-control or desire for healthy bodies than past generations. Why, then, only recently and now suddenly everywhere, are we feeding ourselves into metabolic diseases?
New studies from the fields of psychology, metabolics, and sleep offer practical clues to the overeating puzzle. Summarized in the figure above, controlled clinical trials and laboratory studies from the past two decades highlight some of the most powerful triggers for overeating in our modern lifestyles and environments. The quality and quantity of these studies are sufficient to quantify the magnitude of their overeating effect with reasonable precision.
For most people struggling with weight or eating, one or more of the factors shown in the above Figure are probably contributing.
- Consuming a diet high in ultra-processed foods? If so, studies indicate you're taking in about 500 more calories per day on average than if you were eating the same foods in their whole or minimally processed forms.2
- Is good sleep the exception rather than the rule for you? Laboratory sleep studies indicate that the daily energy intake among people with poor sleep is about 300 calories higher than among good sleepers or those with initially poor sleep who improve their sleep practices.3
- Frequently dining out with friends, family, and coworkers? While socially rewarding, there is a metabolic downside: Most of us are strongly influenced by social norms and the eating behavior of others, significantly increasing our food intake in these settings.4 Keep in mind that the reverse may be true for people struggling with binge eating or emotional eating. For the latter group, eating in isolation instead of socially may be a risk factor for overeating.
- Is your home or workplace a minefield of snacks and sweets? Studies show that convenience—factors such as food visibility and the time and effort needed to obtain the food—makes a surprisingly large difference in how much and how often we eat.5
- Distracted and mindless eating is another modern bugbear for metabolic health. Interestingly, mindless eating appears to have both immediate overeating effects—we eat more in the moment while not paying attention—and delayed effects, as distraction impairs our memory of previous eating, leading us to eat even more later on.6
If you are interested in improving your own metabolic health through better nutrition habits, take two things away from this research summary:
1. These factors, while common, are modifiable. We can consume fewer ultra-processed foods, improve our sleep routines, make better restaurant and social eating choices, reduce food reminders and temptations, and eat more mindfully. We can also consider our individual circumstances to see which factors most apply to us and begin our nutrition changes there.
2. These factors nudge us to overeat unconsciously. While large for the typical person, these effects are generally invisible to us. We simply eat more without any awareness of their influence. Because these factors are difficult to see and feel directly, we must approach them like other powerful but invisible forces, such as gravity. You don't need to see gravity for yourself to wear a parachute when skydiving, and you don't need to feel the pernicious effects of the modern food environment to take corrective action.
1. Executive Summary: Clinical Practice Guideline for the Evaluation and Treatment of Children and Adolescents With Obesityhttps://doi.org/10.1542/peds.2022-060641
2. Hall KD, Ayuketah A, Brychta R, Cai H, Cassimatis T, Chen KY, Chung ST, Costa E, Courville A, Darcey V, Fletcher LA, Forde CG, Gharib AM, Guo J, Howard R, Joseph PV, McGehee S, Ouwerkerk R, Raisinger K, Rozga I, Stagliano M, Walter M, Walter PJ, Yang S, Zhou M. Ultra-Processed Diets Cause Excess Calorie Intake and Weight Gain: An Inpatient Randomized Controlled Trial of Ad Libitum Food Intake. Cell Metab. 2019 Jul 2;30(1):67-77.e3. doi: 10.1016/j.cmet.2019.05.008. Epub 2019 May 16. Erratum in: Cell Metab. 2019 Jul 2;30(1):226.
3. Effect of Sleep Extension on Objectively Assessed Energy Intake Among Adults With Overweight in Real-life Settings: A Randomized Clinical Trial. Tasali E, Wroblewski K, Kahn E, Kilkus J, Schoeller DA. JAMA Intern Med. 2022 Feb 7:e218098. doi: 10.1001/jamainternmed.2021.8098. Online ahead of print. PMID: 35129580.
4. Helen K Ruddock, Jeffrey M Brunstrom, Lenny R Vartanian, Suzanne Higgs, A systematic review and meta-analysis of the social facilitation of eating, The American Journal of Clinical Nutrition, Volume 110, Issue 4, October 2019, Pages 842–861, https://doi.org/10.1093/ajcn/nqz155
5. Painter JE, Wansink B, Hieggelke JB. How visibility and convenience influence candy consumption. Appetite. 2002 Jun;38(3):237-8. doi: 10.1006/appe.2002.0485. PMID: 1207169
6. Robinson E, Aveyard P, Daley A, Jolly K, Lewis A, Lycett D, Higgs S. Eating attentively: a systematic review and meta-analysis of the effect of food intake memory and awareness on eating. Am J Clin Nutr. 2013 Apr;97(4):728-42. doi: 10.3945/ajcn.112.045245.