Tuesday, November 30, 2010

Carbohydrates, low-fat diets, and PCOS

I have hormones on my mind lately.  In an undergraduate nutrition course that I am teaching, we talk a lot about insulin, glucose levels, insulin resistance, and weight gain.  Last week in class we covered metabolic processes and three possible reasons why eating a lot of carbohydrates makes it difficult to lose weight:

First, an insulin primer:
Insulin is a hormone that is released in response to elevated blood-sugar levels and causes your body tissues to take the sugar (called glucose) into it's cells for use by your body.  Whole grain carbohydrates, such as whole wheat, barley, oatmeal, kamut, as well as carbohydrates mixed with fat and protein have moderate surges in blood sugar and thus insulin. Simple carbohydrates, such as in white flour, sugar, corn syrup, and juice, will cause your blood sugar to spike high and thus insulin levels surge as well.

Other functions of insulin:
1. Insulin levels and weight loss:    Insulin decreases hormone-sensitive-lipase activity (HSL). HSL helps to release fat stored in adipose cells into the bloodstream to be taken up by the cells for fatty-acid oxidation and energy production (aka ATP).  Thus, acute or chronic elevated levels of insulin makes it difficult for your body to use stored fat tissue for energy, thereby making it difficult to lose weight.

2.  Carbohydrates and fat synthesis: High insulin levels not only discourage fat breakdown, they also promote synthesis of fat.  This is why people taking insulin shots for diabetes often have some extra fat around their abdomen.

3.  Carbohydrates and triglyceride levels (a predictor of heart disease): High insulin levels can cause elevated triglyceride levels since the body will use excess carbohydrates to make fat in a process called Lipogenesis.  Elevated insulin levels will increase the activity of a certain enzyme (fatty acid synthase), which is used to regulate triglycerides (TG).  We used to think that to decrease your TG levels, you needed to decrease your fat intake.  However, research now shows that decreasing your carbohydrate intake, especially the simple carbs (white flour, white sugar, juice...), is more effective at decreasing TG levels.   In fact, low fat diets and low protein diets, which are higher in carbohydrates, actually increase TG levels.
There is actually an increasing amount of research indicating that low-fat diets, and thus high-carbohydrate diets, are not healthy for you.

At a recent symposium called “The Great Fat Debate: Is There Validity In the Age-Old Dietary Guidance?” at the American Dietetic Association’s (ADA) Food and Nutrition Conference and Expo, four experts presented evidence suggesting that low fat diets may be less healthy than those containing moderate amounts of fat. Dr. Alice Lichtenstein, director of the cardiovascular health laboratory at Tufts University, said "low fat" advice is based on an oversimplification of public health recommendations:

“The emphasis should be on displacing saturated fat and trans fat with unsaturated fat because that is where the data is,…'Displace saturated fat with polyunsaturated fat’ was simplified to ‘low fat’. Then ‘low fat’ became ‘low calorie’. The low fat message is still very pervasive, especially in the lay press.”

Dariush Mozaffarian, MD, DrPH, MPH  from Harvard Medical School showed that saturated fat is not as bad as previously though and replacing saturated fat with carbohydrates – as has been widely recommended in the United States – is likely to raise the risk of cardiovascular disease and obesity.

So what does all of this have to do with women, besides the fact that it seems that every women wants to lose weight and that heart disease is the #1 killer in women? 

Women with Polycystic Ovarian Syndrome often have high insulin levels and have insulin resistance (their insulin is not as effective at lowering blood glucose levels leading to chronically elevated insulin levels).  Besides having cysts on their ovaries, they also tend to be (though are not always) overweight, especially around their abdomen, and have difficulty losing weight, and may have excess hair growth.  Now you are insulin experts and you know why they have a hard time losing weight.  They may also have a difficult time getting pregnant due to the insulin stimulating excess androgens, which are associated with male characteristics and affect the production of female hormones. When they do get pregnant, they are at greater risk of having gestational diabetes.

Now you can see how a low-fat high-carb diet can cause or aggravate this situation by creating more circulating insulin.  Luckily, many women with PCOS are able to get pregnant by modifying their carbohydrate intake (and/or taking medications that help their bodies use insulin better).  Unfortunately, many women that are struggling with infertility are not assessed for PCOS.  If you know someone who is having difficulty getting pregnant and has some of the physical signs of PCOS, you may want to ask her if her doctor ever evaluating her for PCOS.

Next, we will attempt to figure out why women with PCOS may or may not have trouble breastfeeding their babies.  Stay tuned!


  1. Great post, it's so important for women especially to know about these metabolic issues. I want to also point out that there really is a spectrum. I am not overweight, I do not have PCOS and yet I had difficulty getting pregnant, had gestational diabetes, and trouble producing milk after birth. Dr. Mona Gabbay (breastfeeding dr) said it seemed like Insulin Resistance Syndrome which I think is the general term to encompass any issues with resisting insulin (that is - not necessarily specific to PCOS). This "diagnosis" did not and would not show up on any classic infertility test which only further shows how hormones are tricky little buggers and keeping them in line is so important, not just for fertility, but for overall health, considering all the examples you mentioned as the effects of insulin resistance. Thanks again - Shara

  2. Thanks Crunchy Granola for pointing that out. I agree- there is definitely a spectrum of insulin resistance and health problems, and some women have some but not all symptoms of PCOS, depending on how their body compensates for the hormonal imbalance. I also want to point out out that infertility has many causes.