Fasting no longer strictly required for glucose or cholesterol
DEAR DR. ROACH: My nurse practitioner just ordered blood tests, including blood sugar and cholesterol. He said I didn’t need to fast for either of them, but to inform the lab that I wasn’t fasting. This surprised me, since I’ve been fasting for years for these tests. I asked him if I could have coffee, breakfast, etc. No problem, he said. I asked him what was different, and he responded, “There’s new technology out there.” What is your opinion on his advice? — J.S.B.
ANSWER: I’ll start with the blood sugar test, the main purpose of which is to identify abnormally high glucose, either as diabetes or its precursor, prediabetes, also called borderline diabetes or impaired glucose. Both a fasting glucose and a nonfasting glucose can give your clinician a clue, and an abnormal test would usually be followed up with a hemoglobin A1C or glucose tolerance test, which are definitive ways of diagnosing diabetes. A nonfasting glucose is at least as good of a screening test as a fasting glucose, since fasting glucose levels are normal until the condition is pretty advanced.
Blood cholesterol is often measured as total cholesterol, HDL cholesterol, and triglycerides. A formula is used to estimate LDL cholesterol from these, as measuring LDL directly is expensive and time-consuming. Total and HDL cholesterol are not much affected by recent meals, but triglycerides are. Eating before a cholesterol panel usually makes the triglycerides go up, and makes the formula less accurate. Most clinicians still prefer a fasting cholesterol, although there are good data that using non-HDL cholesterol (that’s just the total cholesterol minus the HDL cholesterol) provides as much information about a person’s heart disease risk as a fasting, calculated LDL level.
If the triglycerides themselves are very high, most clinicians will then get a fasting panel. In my own practice, I prefer patients to fast for four hours or so before cholesterol testing (but black coffee/tea and water are always fine). If a patient comes in having just eaten, a total and HDL cholesterol usually gives me all the information I need. Occasionally, I need to get a fasting study anyway.
DEAR DR. ROACH: It seems that my once-weekly steak should not be barbecued, due to carcinogenic factors. A disappointment. How important is this effect? — S.
ANSWER: Grilling meat of any kind leads to the formation of two separate families of cancer-causing chemicals (carcinogens): the heterocyclic amines (HCAs) and polycyclic aromatic hydrocarbons. The old adage remains true that the dose makes the poison. Eating grilled meat less often will reduce your overall exposure, and there are steps you can take during cooking to reduce the generation of these toxic chemicals. These include meticulous cleaning of the grill to get rid of the char already there; marinating your protein, which reduces formation of these toxins; using herbs (likewise); cooking at lower heat or reducing time on the grill by combining with other cooking methods; and cooking lots of grilled vegetables as well (which do not form these toxins when grilling).
I have always recommended reducing, not eliminating, your less-healthy food choices. If you like your grilled steak, make it as safely as possible and enjoy it. The harm from eating these occasionally is small.
Dr. Roach regrets that he is unable to answer individual letters, but will incorporate them in the column whenever possible. Readers may email questions to ToYourGoodHealth@med.cornell.edu or send mail to 628 Virginia Dr., Orlando, FL 32803.