Understanding the science of weight loss

My Wife (aged 61 - current weight 208 pounds, height 5 ft 9 inches) has been trying to lose weight for many years following treatment for depression (Seroxat) at which time her weight had increased to about 250 pounds.  However, in spite of rigorous dieting, her weight loss seems to have come to a standstill at the level of about 208 pounds.  She would like to achieve a weight of about 160 pounds thus bringing her BMI to lower than the "magic" level of 25.

During my University chemistry degree, I was taught the "law of conservation of matter" which, as I am sure you know, basically states that "matter (and energy??) cannot be created or destroyed - overall".  When seeeking advice on a weight loss regime, my Wife previously underwent a "calorific assessment" which determined that her required daily calorie intake was about 1500 which was quite low and indicated a slowish metabolism.  She was told that in a normal person a "calorie deficit" of 7500 would equate to a weight loss of ~ one kilo = 2.2 pounds.

My Wife keeps a meticulous diary of what she eats and I know that she does not "cheat" on her diet.  Her usual daily calorie intake is about 800 which equates to a daily calorie deficit of 700 = a weekly deficit of 4900 calories.  This should "reward" her with a weekly weight loss of approx 1.5 pounds especially as she enhances her calorie utilisation by gentle work-outs at the gym.  

So, according to the law of conservation of matter/energy, her net energy intake is less than her net energy utilisation and this should (MUST??) be reflected by a weight loss at the approximate rate of 2.2 pounds per 7500 calories.  But this just does not seem to be happening.  On a day by day or single week basis I could imagine that this ratio is not attained due to distortions in water/fluid levels etc - but surely over a period of months one would expect the continuing calorie deficit to correspond to the above mathematical "weight loss formula"?  We both just can't understand it.

I wonder whether you could elaborate on:-

a) whether you believe that the above scientific statements on the law of conservation of matter - and the calorie deficit/weight loss ratio of minus 7500 calories = 2.2 pounds weight loss - are indeed fundamentally correct?

b) or are there exceptions which might apply and under what circumstances?

c) is it safe for my Wife to decrease her calorie intake further from a daily level of 800 as long as she eats foods with essential minerals and vitamins etc?

d) can you offer any other explanations and can you suggest any further medical tests and/or modifications to her weight loss strategy that will prove more successful.  For her it is frustrating and demotivating to "suffer the pain" (of dieting) but not to achieve the "gain" (of weight loss)!!

e) does all surplus body fat (even if not evenly distributed over the body) disappear in successful weight loss?

f) any other suggestions/wisdom please!!  Many thanks.

[Kevin Pho, MD]

To answer your questions:
1) It does make sense that the more calories going out than taking in would result in weight loss.  However, I'm not sure if you could quantify the weight loss that exactly - I am not a nutritionist so I cannot be sure.

2) I would think that the amount of calories burned may vary from patient to patient.  Also, various underlying diseases (i.e. thyroid disease) can influence weight loss.

3) The recommended daily calorie intake for women is 1940 calories per day.  A daily caloric intake of 800 calories is quite low, and I would not recommend decreasing this.

4) I would test for underlying disease - such as thyroid tests, a metabolic panel and a blood count.

5) The body will still need some fat - so you cannot expect 100% of the fat to disappear after a successful weight loss program.

Followup with your personal physician is essential.

This answer is not intended as and does not substitute for medical advice - the information presented is for patient education only. Please see your personal physician for further evaluation of your individual case.

Kevin, M.D.
Medical Weblog:
kevinmd_b

[lmroswell]

With her caloric intake at only 800 calories, she may have a very low metablolism.  The body thinks it is basically starving, so the body's metabolic rate has decreased.  Also, with dieting, some people tend to plateau for a while.  When this has happened to me, I try to kick start my metabolism by eating a little more, more frequently, and increase my activity level.