Hi Eve,
our metabolisms work differently depending on how they have been programmed and trained - by our ancestors and their conflicts, by our own conflicts, by our values, by our beliefs, and by our habits. There are certain conflicts that especially impact our weight: 
*brain stem "((Digestive - Liver - Parenchyma|starvation))" fear makes us save and store energy more efficiently (by getting fat). We might also get greedy and overeat, but not necessarily.
*brain stem "((Urinary - Kidneys - Collecting Tubules|abandonment))" makes us retain water
*brain stem "((Endocrine - Thyroid - Follicular Epithelium|need to get faster))" makes us burn lots of energy so these people always keep thin whatever they eat
*cortex "((Endocrine - Pancreas - Alpha Islet Cells|resistance/disgus))t" avoidance strategies can give us cravings
*medulla "inner fight" about the ((Endocrine - Adrenal Gland - Cortex|way to follow)) can also give us cravings