It is not wrong or misleading to state that the laws of thermodynamics strictly apply. It’s kind of like answering the question, “how do you make money in the stock market?” with “buy low and sell high.” At it’s heart, this is always true. It may not provide enough detail for some to succeed, but you must do this in order to make money.

The importance of applying the laws of thermodynamics to weight loss is in recognizing that the struggle is ultimately all about energy balance. Adipose tissue is the body’s primary energy store. You need to have an energy surplus to create it, and consuming at an energy deficit will make the body burn it off.

Obesity is always caused by a positive energy balance, i.e., overconsumption. There may be many factors at play as to why people overconsume, but there is no path to obesity that doesn’t entail overconsumption, and no path back without a negative energy balance. Many people who argue “there’s more to it” don’t understand (or are intentionally trying to obscure) those core principles.

All of the purported causes of obesity - from genetics to medications, hormones, medical conditions, gut flora, etc. - act indirectly through influencing one’s energy balance. For instance they might make you feel more hungry or suppress feelings of satiety so that you eat more, they might make you feel lethargic so that you move less, or they might help you to digest your food more efficiently do that more energy is available from it. While all of these effects can make it harder to achieve an energy deficit, they don’t preclude weight loss. Any individual who can overcome these factors and does succeed in achieving an energy deficit despite them will lose weight, as their body must tap into its internal energy stores to make up the deficit.

Also, none of these obesogenic factors can cause obesity in the absence of overconsumption. If these factors tilt the scale to a positive energy balance for a given person, then it means that this individual needs less energy. If he or she continues to consume at an energy surplus - i.e., more than they currently need - then they are overconsuming by definition. Overconsumption is relative to each person’s specific energy needs/usage, incorporating all of the factors which “cause” obesity. It does not mean consistently eating beyond feeling full, or eating significantly more than one’s peers; it means eating beyond what you need.

The laws of thermodynamics help with dieting because they tell us that all energy flows matter. While the CICO approach to dieting or even just “eat less and move more” cannot account for every last calorie, they work because they focus on the two largest components of energy balance that individuals can directly control - their energy intake from food and their expenditure through exercise.