Doodle may be right but I couldn't find any where they associated weight loss with the formation of stretch marks. Below is some info I found on MSN's Web MD.
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Alternative Names :
stretch marks; stria atrophica; striae distensae

Definition:
Skin defects that look like bands or lines, associated with rapid growth or certain diseases or conditions.

Common Causes:
pregnancy
puberty
obesity
Cushing's syndrome
iatrogenic Cushing syndrome
topical corticosteroid overuse
Prader-Willi Syndrome
Laurence-Moon-Biedel syndrome
Ehlers-Danlos syndrome

Note: There may be other causes of stria. This list is not all inclusive, and the causes are not presented in order of likelihood. The causes of this symptom can include unlikely diseases and medications. Furthermore, the causes may vary based on age and gender of the affected person, as well as on the specific characteristics of the symptom such as location, quality, time course, aggravating factors, relieving factors, and associated complaints. Use the Symptom Analysis option to explore the possible explanations for stria, occurring alone or in combination with other problems.


Considerations :
Stretch marks can appear when there is rapid stretching of the skin. They are often associated with the abdominal enlargement of pregnancy. They can be found in children who have become rapidly obese. They may also occur during the rapid growth of puberty in males and females. Stria are most commonly located on the breasts, hips, thighs, buttocks, abdomen, and flank.
Stretch marks appear as parallel streaks of red, thinned glossy skin that over time become whitish and scarlike in appearance. The stretch marks may be slightly depressed and have a different texture than normal skin.
Stria may also occur as a result of abnormal collagen formation, or a result of medications or chemicals that interfere with collagen formation. They may also be associated with prolonged administration of cortisone compounds, diabetes mellitus, Cushing disease, and post-pregnancy.

Home Care:
There is no specific care for stretch marks. Advertised creams and salves to prevent stretch marks during pregnancy are of little value. However, the marks often will disappear after the cause of the skin stretching is gone. Avoiding rapid weight gain helps in the case of stretch marks associated with obesity.

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Hope this helps!