&gt;There has to be more to it that calories in - calories out = weigh gain or loss.<p>There is. Read the &quot;physiology&quot; chapter at <a href="https:&#x2F;&#x2F;en.wikipedia.org&#x2F;wiki&#x2F;Adipose_tissue" rel="nofollow">https:&#x2F;&#x2F;en.wikipedia.org&#x2F;wiki&#x2F;Adipose_tissue</a><p>TLDR: Blood sugar spikes above certain level are toxic, so the body responds with an emergency action of stashing the sugar wherever possible, including muscle, liver, and fat tissue. The former two are rather limited in their capacity, while the latter is unlimited. At the &quot;hardware&quot; level, that&#x27;s all there is to obesity.<p>At the higher levels there are other emerging phenomena:<p>- This process is prone to overshooting the sugar egress, creating a &quot;sugar crash&quot;, which has to lead to another sugar binge. This becomes an unhealthy see-saw. Note that the fat cells are consuming sugar but they can&#x27;t release it back, they can only release fatty acids, hence sugar deficit must be replenished through food.<p>- The see-saw may end up messing the appetite and the balance of hormones that partake in regulating the metabolism. This yields the so-called &quot;metabolic syndrome&quot; with all its co-morbid factors: <a href="https:&#x2F;&#x2F;en.wikipedia.org&#x2F;wiki&#x2F;Metabolic_syndrome" rel="nofollow">https:&#x2F;&#x2F;en.wikipedia.org&#x2F;wiki&#x2F;Metabolic_syndrome</a><p>- The hormonal imbalance changes the person&#x27;s appetite, creating a vicious cycle.<p>Simple sugars are addictive. Just try going without to see how bad it can get - keep eating the fats, the meats, the complex carbs, just cut out the sugars, starches, and flours.