I've posted before about my belief that leptin resistance (and later, obesity) occurs as a result of elevated serum triglycerides blocking the passage of leptin across the blood-brain barrier:
Heavy fructose consumption via sweetened drinks happens to be an excellent way to boost triglycerides. I have heard many anecdotes of people (males) who stopped drinking soda and dropped something like 30 pounds without making any other change. I've seen far fewer females make such a claim. In correcting their hypertriglyceridemia, these males opened the passage of (a significant amount now that they're overweight) leptin to the hypothalamus. Appetite is greatly reduced and weight is lost rapidly.
One additional result of the weight loss for these males is an increase in testosterone that was depressed due to upregulated aromatase activity (which is an enzyme that converts testosterone to estradiol and is more active with a greater fat mass in males). Testosterone actually decreases the concentration of leptin (women tend to have 3x as much, even when fat amounts are accounted for) which you would think would decrease satiety, but testosterone also upregulates lipolysis. Assuming that triglycerides don't rise again, males have an endocrine protection put back in place to prevent a return to obesity.
I have seen it written many times here and elsewhere in the paleosphere where a female has done the exact same thing as her boyfriend or as other paleo-eating males have done with negligible results. These women generally have dropped their triglycerides down to excellent levels, but it doesn't make a difference. It is my contention that paleo fails for weight loss in women due to hypogonadism, to too little estrogen.
Peri- and post-menopausal women of course have less estogen than younger females and an increased risk of obesity: http://www.ncbi.nlm.nih.gov/pubmed/14567150 http://www.nature.com/oby/journal/v9/n10/abs/oby200181a.html
Mice that cannot produce estrogen become obese: http://endo.endojournals.org/content/141/11/4295.short
I believe that the reason why this hypogonadism may occur in women who are not near menopause is due to a zinc deficiency. Zinc is needed for the synthesis of estrogen: http://www.springerlink.com/content/q41833xm48214247/ and is excreted (along with iron) during menstruation. If a female has endured a period of time in the past where she has been menstruating, exercising heavily and not consuming much zinc-dense foods (vegetarian/vegan diet) she could conceivably deplete her zinc stores and create a deficiency that interferes with sex hormone synthesis.
I am positing that a correction of a zinc deficiency would increase serum estrogen levels, increase leptin: http://joe.endocrinology-journals.org/content/154/2/285.short and reduce body fat levels. Because triglycerides will likely be greatly reduced by this point, everything should be in place for rapid fat loss. 50 mg of zinc picolinate taken on an empty stomach between meals once a day should in time correct this deficiency and bring levels of estrogen back to their correct position.
In the absence of a properly functioning endocrine system, certain coping mechanisms such as a forced reduction in the daily insulin area under the curve via ZC/VLC in order to maximize lipolysis can be employed with obvious success, but this is ultimately not a necessary state for an individual with intact endocrine function. I don't believe that these individuals have a "broken metabolism" or a "burned out pancreas" but rather under-performing ovaries that need more zinc.
That all being said, this seems too simple for my tastes, so I'm looking for some exceptions from women who have mid- high-normal or high levels of estrogen and still experience great difficulty in not being overweight with a mixed diet.