Kidney stones (and obesity)

(continued from a previous entry, The excesses of modern life and kidney stones)

4. Weight

The NY Times article “A Rise in Kidney Stones Is Seen in U.S. Children” alludes to the rise in obesity as a likely contributor to an increase in kidney stones but neglects to provide an explanation.

A simple argument, of course, would implicate known risk factors, such as a higher intake of salt and protein and insufficient intake of water, but the assertion of the article and many experts is that obesity increases the risk of kidney stones independent of typical risk factors.

How might that be? The link is insulin resistance.

Insulin resistance

Insulin resistance is the insufficient response of the body to the insulin that the pancreas secretes. That is, normally, in proportion to our meals the pancreas (to assist in regulating our metabolism of food) secretes insulin that initiates important chains of events in our muscle, liver, and fat tissues. In the setting of insulin resistance, the pancreas secretes the insulin, but the body's tissue, rather than jumping to attention and reacting appropriately, merely shrugs. Again, the body is resistant to the insulin the pancreas is secreting. To overcome this indifference, the pancreas must secrete more insulin.

There are several causes of insulin resistance, including genetic, but a growing cause is obesity. (Not all obese individuals develop insulin resistance, and proper diet, exercise and weight loss can lower insulin resistance.)

The problem with insulin resistance is that it is associated with multiple medical problems, such as diabetes mellitus (often the first step on the road to diabetes, developing even decades before diabetes is diagnosed), hypertension, and cardiovascular disease.

Uric acid

Less well known is the association between insulin resistance and high uric acid levels in the body. High levels of uric acid in the blood can lead to the infamous gout, a painful, inflammatory arthritis.

In the urine high levels predispose to kidney stones - not only to uric acid stones but also to almost all other types of kidney stones. Microscopic crystals of uric acid can act as the tiny seed or nucleus around which other minerals are able to amass, thereby provoking the formation of other types of kidney stones.

Bottom line

Obesity is linked to insulin resistance and its association with high levels of uric acid in the urine, which contribute to kidney stones.

(More on insulin resistance in a future entry.)