&gt; A calorie surplus is pretty necessary for a substantial weight gain.<p>Sure, but that still doesn&#x27;t justify the upthread claim &quot;When your calories in is greater than your calories out, you gain fat.&quot;<p>You can maintain a calorie surplus and not gain fat, and if you are intending to gain a substantial quantity of lean body mass, you will need to. (That you can gain fat, within a certain range, while losing lean body mass on a calorie deficit was a less important aspect of my response; the key part was that the claim &quot;moar calories =&gt; moar fat&quot; is significantly wrong.<p>&gt; You seem to do this a lot, writing some pedantic elaboration on the wording of a comment while carefully ignoring the thrust of the meaning.<p>The thrust of the meaning was that calorie surplus&#x2F;deficit alone controls body fat. This is fundamentally and critically wrong, because it ignores the fact that activity patterns and other factors will control whether a calories surplus (for example) manifests in fat gain (with constant or decreasing muscle) or muscle gain (with constant or decreasing fat) or both muscle and fat gain in some ratio.