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Intermittent fasting is the latest popular diet. It really does change metabolism, but its effects on bone health vary. Here is what women need to know about intermittent fasting and osteoporosis, especially if they have diabetes.

Intermittent fasting is the latest popular response to the obesity epidemic, which has inspired a cottage industry of weight loss diets. Unlike many other diets, intermittent fasting works by giving the body's metabolic processes a vacation from food, so they have time to realign themselves. There are many documented benefits of intermittent fasts. For women at risk of osteoporosis, there are indications that using this technique to get insulin resistance under control may prevent loss of bone mineral density.

What is intermittent fasting?

Intermittent fasting isn't really a diet. It's more of a non-diet. As the name suggests, intermittent fasting involves eating no food at all. Water, zero-calorie teas and naturally carbonated zero-calorie beverages are permitted.

The "intermittent" part of intermittent fasting refers to the length of the fast. This technique usually makes a difference if food and nutritional beverages are avoided for at least 12 hours. That's as simple as avoiding snacks after dinner. Cells throughout the body have a chance to renew themselves through the process of autophagy, breaking down old defective proteins into amino acids to build new structures, if they do not have to process incoming nutrients for about 17 hours.

To make sure autophagy occurs, most intermittent fasting experts recommend going 24 hours without food, but making sure to stay hydrated. That period usually involves skipping dinner and then skipping breakfast and lunch the next day. You won't lose weight if you super-size the meal you eat when you stop your fast. But the metabolic benefits of intermittent fasting are yours even if you do. Your body changes your metabolism while you fast.

What does intermittent fasting do for your metabolism?

Hundreds of millions of people don't have type 2 diabetes but do have a problem with the use of insulin called insulin resistance. Whether or not they are "prediabetic," these otherwise healthy people's bodies make too much insulin because their cells don't respond to it properly. When their blood sugar levels go up after a meal, the beta-cells of the pancreas release large amounts of insulin. To keep from being flooded with sugar, liver and muscle cells shut down receptors for insulin. This keeps blood sugar levels from going down quickly, so the pancreas releases still more insulin. In turn, cells elsewhere in the body shut down still more insulin receptors.

The process continues night and day, unless, of course, it is interrupted by a short-term fast. Intermittent fasting gives the body a chance to reset.

Intermittent fasting:

  • Promotes energy production in brown fat. When you eat normally, you tap your brown fat reserves only when you are cold and shiver. You'll lose brown fat mass without shivering during intermittent fasting.
  • Changes the ratios of different kinds of bacteria in your colon. It increases the number of Firmicutes bacteria, and decreases the number of Bacteroidetes​ bacteria. When you have more Firmicutes in your gut, your body absorbs less sugar from food the next time you eat.
  • Makes cells across your body more sensitive to insulin. This last point requires a little explanation.

When your body becomes less resistant to insulin, your pancreas makes less insulin. This helps to "unlock" fatty acids stored in your fat cells so they can be liquefied, circulated to your muscles, and burned when you exercise. This changes sugar-burning exercise to fat-burning exercise. Losing weight, especially losing fat, becomes easier when you diet and exercise. You still need to take in fewer calories than you burn (over the long term),but at least you can burn fat and keep muscle.

This has to be a good thing for your bones, doesn't it? Well, the answer is "maybe."

What are the effects of intermittent fasting on bone health?

Research studies have found different sets of results of intermittent fasting on bone health:

  • In healthy women of European descent, insulin resistance isn't necessarily a bad thing for bone health. Heavier, non-diabetic women have smaller but denser bones that are resistant to fractures. Intermittent fasting probably doesn't hut bone health, but it won't help it.
  • In healthy women of northeast Asian descent, insulin resistance isn't a good thing for bone health. It seems to have little or no relationship to osteoporosis.
  • When insulin resistance has progressed to type 2 diabetes, intermittent fasting holds significant benefits for bone health and preventing osteoporosis.

Women who have type 2 diabetes tend to get fat deposits in their bones. Anything that depletes those fat deposits, as long as the bone-building process is still healthy, helps to prevent fractures.

And women who have type 2 diabetes tend to build up HbA1C, a measurement of glycation end products. These sticky proteins interfere with the collagen framework on which bones deposit mineral crystals. Taking a break from food lowers the production of glycation end products and makes bones stronger.

So the answer to whether intermittent fasting makes a difference for women's bone health is "It depends". Women who have type 2 diabetes can use intermittent fasting to improve bone health and diabetes at the same time.

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  • Shanbhogue VV, Finkelstein JS, Bouxsein ML, Yu EW. Association Between Insulin Resistance and Bone Structure in Nondiabetic Postmenopausal Women. J Clin Endocrinol Metab. 2016 Aug.101(8):3114-22. doi: 10.1210/jc.2016-1726. Epub 2016 May 31. PMID: 27243136.
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  • Photo courtesy of SteadyHealth

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