Rerun: To let low-carb right, you must check POSTPRANDIAL blood sugars

Checking postprandial (after-eating) blood sugars yields extraordinary advantage in creating better diets for many people.

This idea has proven so powerful that I am running a previous Heart Scan Blog post on this practice to bring any newcomers up-to-date on this powerful way to improve diet, lose weight, reduce small LDL, reduce triglycerides, and reduce blood pressure.

To get low-carb right, you need to check blood sugars

Reducing your carbohydrate exposure, particularly to wheat, cornstarch, and sucrose (table sugar), helps with weight loss; reduction of triglycerides, small LDL, and c-reactive protein; increases HDL; reduces blood pressure. There should be no remaining doubt on these effects.

However, I am going to propose that you cannot truly get your low-carb diet right without checking blood sugars. Let me explain.

Carbohydrates are the dominant driver of blood sugar (glucose) after eating. But it's clear that we also obtain some wonderfully healthy nutrients from carbohydrate sources: Think anthocyanins from blueberries and pomegranates, vitamin C from citrus, and soluble fiber from beans. There are many good things in carbohydrate foods.

How do we weigh the need to reduce carbohydrates with their benefits?

Blood sugar after eating ("postprandial") is the best index of carbohydrate metabolism we have (not fasting blood sugar). It also provides an indirect gauge of small LDL. Checking your blood sugar (glucose) has become an easy and relatively inexpensive tool that just about anybody can incorporate into health habits. More often than not, it can also provide you with some unexpected insights about your response to diet.

If you’re not a diabetic, why bother checking blood sugar? New studies have documented the increased likelihood of cardiovascular events with increased postprandial blood sugars well below the ranges regarded as diabetic. A blood sugar level of 140 mg/dl after a meal carries 30-60% increased (relative) risk for heart attack and other events. The increase in risk begins at even lower levels, perhaps 110 mg/dl or lower after-eating.

We use a one-hour after eating blood sugar to gauge the effects of a meal. If, for instance, your dinner of baked chicken, asparagus brushed with olive oil, sauteed mushrooms, mashed potatoes, and a piece of Italian bread yields a one-hour blood sugar of 155 mg/dl, you know that something is wrong. (This is far more common than most people think.)

Doing this myself, I have been shocked at the times I've had an unexpectedly high blood sugar from seemingly "safe' foods, or when a store- or restaurant-bought meal had some concealed source of sugar or carbohydrate. (I recently had a restaurant meal of a turkey burger with cheese, mixed salad with balsamic vinegar dressing, along with a few bites of my wife's veggie omelet. Blood sugar one hour later: 127 mg/dl. I believe sugar added to the salad dressing was the culprit.)

You can now purchase your own blood glucose monitor at stores like Walmart and Walgreens for $10-20. You will also need to purchase the fingerstick lancets and test strips; the test strips are the most costly part of the picture, usually running $0.50 to $1.00 per test strip. But since people without diabetes check their blood sugar only occasionally, the cost of the test strips is, over time, modest. I've had several devices over the years, but my current favorite for ease-of-use is the LifeScan OneTouch UltraMini that cost me $18.99 at Walgreens.

Checking after-meal blood sugars is, in my view, a powerful means of managing diet when reducing carbohydrate exposure is your goal. It provides immediate feedback on the carbohydrate aspect of your diet, allowing you to adjust and tweak carbohydrate intake to your individual metabolism.

Comments (12) -

  • Chris Keller

    4/1/2010 9:56:58 PM |

    I understand low carb diets in general, but the way you talk about postprandial blood sugar levels, what can you eat?  

    You continuously point out that foods you didn't think would cause high blood sugars do (is it because of the actual food or hidden ingredients like sugar), so what's on your acceptable list?  (in general).  I realize everyone's body will react slightly differently...

  • kris

    4/2/2010 2:41:20 AM |

    Dr. davis,
    I always follow your valuable blogs. please keep up the good work. here is the link to the type of meals to cut down on the carbs.checkk it out.

  • Anonymous

    4/2/2010 8:29:25 AM |

    My suspicion is that the balsamic vinegar was the culprit. Some brands are extremely sweet because they have added sugar.

  • Anonymous

    4/2/2010 12:54:14 PM |

    Dr. Davis,
    What is an acceptable blood glucose level after a meal? What goal do you recommend for your patients?

  • DrStrange

    4/2/2010 4:55:55 PM |

    I don't know about the Life Scan bg monitor but I do know that some monitors are totally inadequate!  Walmart Relion for one.  I have one and can easily do 2 tests within a few seconds of each other and get readings of 180 and 135!!!!  AcuCheck by Aviva which I also have has never given me a multiple reading spread of more that about 5 points, and that is a 3 year old meter.  You don't do yourself any favors by going cheap. It you have a sympathetic doc who will write a scrip you can get meter for free and have a big chunk of test strip cost covered.

  • Michael Barker

    4/2/2010 9:17:23 PM |

    You should add this one caveat. Fructose and its various aliases does not raise blood sugar immediately. It will do so eventually when it screws up your liver.


  • Narda

    4/3/2010 2:33:53 PM |

    Regarding the dressing...I learned decades ago in high school biology that vinegar turns to sugar in the blood. Is this true?

  • TedHutchinson

    4/3/2010 4:11:09 PM |

    Regulars will know I bought a meter after the first appearance of this post. I was regularly over 8.6 = 155 at one hour.
    Went to doctor fasting blood glucose 4.9= 88.2 and HbA1c 5.6 = 100.8 which my doctor thought fine.
    I pointed out the day before and day after my meter was reported much higher numbers, he suggested a fasting oral glucose tolerance test for which I had to prepare by consuming 175mg carbs daily for 3 days, which I did gaining several lbs.
    However 2hr reading 5.8 = 105
    My meter reported  11.3 =203.4 at 1 hr but I peaked at 17.3 = 311.4 the following meal.
    Inflammation markers and metabolic characteristics of subjects with one-hour plasma glucose levels
    this paper suggests that Elevated one hour plasma glucose (1hPG) in people with normal glucose tolerance and pre-DM subjects is associated to subclinical inflammation, high lipid ratios and insulin resistance. Therefore, 1hPG >155 ( = 8.6) could be considered a new 'marker' for cardiovascular risk.
    Medscape article on same paper.
    One-Hour Plasma Glucose Levels May Be a Marker for Cardiovascular Risk

    So as far as my doctor is concerned I've no problems whatsoever. It seems to me absurd that if I followed his advice I'd be a diabetic basket case and the situation would be almost irretrievable before they will take any action.
    I've been a bit stricter with the carbs and have followed some other suggestions so have managed to keep 1hr numbers below 6.7 = 120

  • Anonymous

    4/6/2010 1:54:16 PM |

    So if the peak blood glucose is important, then things that lower it are generally good? Foods with a low glycemic index, which are slow release?  Polyphenols like green tea and red wine, which inhibit amylase and reduce the sugar spike?

  • Anonymous

    4/8/2010 11:21:34 AM |

    You have a choice?

    To die of heart disease or alzheimers?

    "Those who drank juice three or more times per week experienced a 76 percent reduced risk for Alzheimer's. Those who drank juice once or twice a week experienced a 16 percent reduced risk."

    But various polyphenols have been show to also modify glucose levels in some cases?

  • jpatti

    5/7/2010 7:46:47 AM |

    What you can eat is *based* on postprandial bg.  

    My husband can eat 1/6th of a 2-layer chocolate cake.  

    I can eat around 20g carb at breakfast, 40g at lunch and dinner, and that requires insulin injections.

    We're all different, you have to test yourself:

  • Anonymous

    4/20/2011 12:08:55 PM |

    After finding your blog, I purchased a blood glucose monitor and have been checking my post-prandial blood sugars 1 and 2 hours after eating a meal.  I am also checking some fasting a.m. blood sugars.

    I am obese, though I have lost 49 pounds by reducing overall carb intake and eliminating all grains, sugars and processed foods.  I eat primarily a whole food diet other than a little (.25 oz.) of very dark chocolate a day (85%).

    My post-prandial 1 hour are between 90-110 most meals, and 2 hours are almost always below 100.  However, I am noticing that my fasting blood sugars are rising, sometimes above 100.

    Should I be concerned?  Is there anything I can be doing differently to reduce the insulin resistance that seems to be developing due to carb restriction?  Total carb intake daily is around 50 grams, including fiber.

    Stephanie A.