Your partner isn't eating enough.  1200-1300 calories a day isn't enough for an adult.  It should be closer to 2000.  Of course, that amount varies by gender, age, height, activity level, medical conditions, current injuries, etc. The Harris-Benedict equations will let you calculate basal energy expenditure, meaning how much energy the body needs just for the normal metabolic activity of the body, like breathing, heartbeat, enzyme function, temperature homeostasis, etc.  This is assuming that you're parked in bed all day doing absolutely nothing but existing. Men 66.5 + [13.75 * weight (kg)] + [5 * height (cm)] - [6.76 * age] Women 655.1 + [9.56 * weight (kg)] + [1.85 * height (cm)] - [4.68 * age] As you can see, the number is relative low.  Keep in mind that this is just what your body needs to  keep you alive if you're doing absolutely nothing else.  The second you move, you need to start adding calories.  If you're underweight, you add even more to get up to the correct body weight.  If you're trying to lose weight, you remove calories.  Basic CICO.  I'm not sure why fatties can't understand this incredibly simple concept.