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The main point of this article is that simply reducing calorie intake often does not lead to fat loss. This is because lowering calories consumed causes the body to lower its metabolic rate. The body regulates fat mass much like a thermostat, adjusting energy expenditure to defend against changes. So calorie restriction tends to be ineffective for long-term weight loss.
The Energy Balance Equation
The energy balance equation states that weight is determined by calories in versus calories out. More simply, it is the idea that to lose fat, you need to eat fewer calories than you burn. This seems intuitively true. However, it ignores a key factor – that cutting calories affects the calories out part of the equation as well.
The Flaw of Simplistic Thinking
Many people assume that eating less will directly lead to fat loss. But this thinking is too simplistic, because it fails to account for changes in energy expenditure. Decreasing calories consumed often decreases calories burned. So the two sides of the energy balance equation change together, leaving fat levels unchanged.
The Financial Analogy
An analogy with business revenues and expenses illustrates the flaw. Cutting business revenues does not guarantee increased profits. That’s because costs often drop as well. For weight loss, reducing food intake (calories in) often reduces metabolic rate (calories out). So like revenues and costs, the two sides of the energy balance equation tend to move together, thwarting fat loss.
The Biology of Human Starvation Study
An influential semi-starvation study in 1944 by Dr. Ancel Keys revealed important findings. Participants consumed 40% fewer calories, which initially led to weight loss. However, their metabolic rate soon plummeted by a similar 40%. They felt tired, cold, and hungry as their bodies conserved energy. Food became an obsession for them.
Metabolic Slowdown with Calorie Reduction
This metabolic adaptation to calorie reduction has been repeatedly confirmed. Eating less causes burning fewer calories, making weight loss plateau. While predictable biologically, this metabolic slowdown is often blamed on personal failure rather than basic human physiology.
The Biggest Loser Study
In 2012, contestants on The Biggest Loser who lost large amounts of weight also experienced steep reductions in metabolic rate. Despite drastic fat loss, they burned hundreds fewer calories per day. This exemplifies how calorie restriction slows metabolism, fighting against sustained weight loss.
Reduced Metabolism Sabotages Weight Loss
In summary, eating less calories triggers adaptive thermogenesis – a slowing of resting metabolism. So calories out drops as calories in drops. This metabolic slowdown then stalls further weight loss. Despite being a normal biological response, it is often perceived as a lack of willpower or compliance.
Obesity is Not Just a Willpower Problem
Given the current obesity epidemic, it is implausible that willpower has suddenly plummeted. Instead, a flawed system of dietary advice and an obesogenic environment better explain rising obesity levels. The body’s fat thermostat often becomes elevated, making weight loss an uphill battle.
Conclusion
Reducing caloric intake almost invariably reduces metabolic rate. Therefore, weight loss efforts should focus more on resetting the body’s fat thermostat, rather than pursuing an unsustainable calorie deficit through sheer willpower. Sustained fat loss requires shifting biological levers, not just eating less.
Source: Dr. Jason Fung
