A caloric deficit reliably leads to a reduction in weight, but the situation is more complicated.<p>Diet feeds back into resting energy expenditure (REE).  Namely, a low-carb diet leads to higher REE than e.g. a low-fat diet.<p><i></i>Effects of Dietary Composition on Energy Expenditure During Weight-Loss Maintenance<i></i>
<a href="https:&#x2F;&#x2F;jama.jamanetwork.com&#x2F;article.aspx?articleid=1199154#COMMENT" rel="nofollow">https:&#x2F;&#x2F;jama.jamanetwork.com&#x2F;article.aspx?articleid=1199154#...</a><p>&gt; Conclusion: Among overweight and obese young adults compared with pre–weight-loss energy expenditure, isocaloric feeding following 10% to 15% weight loss resulted in decreases in REE and TEE that were greatest with the low-fat diet, intermediate with the low–glycemic index diet, and least with the very low-carbohydrate diet.<p>This is a change of REE on the order of ~10%, so not huge, but definitely significant.<p>When eating a similar diet, eating less certainly works.  However, affecting TDEE through diet and exercise is an important consideration as well, and may be easier and more maintainable than caloric restriction.  There are also issues with satiety and diet that are important for weight loss.<p>Calories In -&gt; Calories Out  should only be a response to people who claim to be unable to control their weight.  If they control how much they eat, they can control their weight.  It does not make it helpful weight loss advice, though.