Blood sugar: Fasting vs. postprandial

Peter's fasting blood glucose: 89 mg/dl--perfect.

After one whole wheat bagel, apple, black coffee: 157 mg/dl--diabetic-range.

How common is this: Normal fasting blood sugar with diabetic range postprandial (after-eating) blood sugar?

It is shockingly common.

The endocrinologists have known this for some years, since a number of studies using oral glucose tolerance testing (OGTT) have demonstrated that fasting glucose is not a good method of screening people for diabetes or pre-diabetes, nor does it predict the magnitude of postprandial glucose. (In an OGTT, you usually drink 75 grams of glucose as a cola drink, followed by blood sugar checks. The conventional cut off for "impaired glucose tolerance" is 140-200 mg/dl; diabetes is 200 mg/dl or greater.) People with glucose levels during OGTT as high as 200 mg/dl may have normal fasting values below 100 mg/dl.

High postprandial glucose values are a coronary risk factor. While conventional guidelines say that a postprandial glucose (i.e., during OGTT) of 140 mg/dl or greater is a concern, coronary risk starts well below this. Risk is increased approximately 50% at 126 mg/dl. Risk may begin with postprandial glucoses as low as 100 mg/dl.

For this reason, postprandial (not OGTT) glucose checks are becoming an integral part of the Track Your Plaque program. We encourage postprandial blood glucose checks, followed by efforts to reduce postprandial glucose if they are high. More on this in future.

Comments (23) -

  • Jenny

    2/5/2010 2:26:07 PM |

    Dr. Davis,

    157 one hour after eating is NOT the diabetic range by any standard.

    To be considered diabetic a person must go over 200 mg/dl.

    The data collected by Dr. Christensen's CGMS studies suggest that 160 at one hour is the top of the normal range if the blood sugar drops back in the next hour.

    That 157 is "prediabetic" though the term is a misnomer because most people with "prediabetic" blood sugars will NEVER become diabetic since they lack the necessary genetic flaws that produce true diabetes.

    I mention this not to discourage people from lowering their carb intake and blood sugar--that's a very good tack to take, but because I hear from hundreds of people who obsess about being diabetic when they are not some of whom end up spending a lot of unnecessary money on doctor appointments that produce nothing useful.

    The latest research suggests that keeping blood sugar under 155 mg/dl at all times will control the blood sugar related component of heart disease. But to diagnose even "pre-diabetes" you have to look at the 2 hour reading. It is the inability to reduce a spike within 2 hours that appears to be associated with most diabetic complications.

  • Anonymous

    2/5/2010 2:57:04 PM |

    When do you recommend taking postprandial glucose measurements?  45 mintues, 1 hour, 2 hours?  And are they timed from the start of the meal, or the end of the meal?

  • Onschedule

    2/5/2010 3:57:11 PM |

    For those of us who do not eat wheat, avoid grains, and restrict sugar intake, it is important to know that the pancreas gets used to dispensing a certain (lower) amount of insulin. Therefore, if you decide to test postprandial glucose after eating a meal with significantly more carbohydrate/sugar, be aware that you will likely get scary-high readings. When preparing for an oral glucose tolerance test, a patient is normally told "do not restrict carbs" or "eat a normal diet" during the week preceding the test in order to allow the pancreas to adjust its phase 1 insulin response. (when they say "normal diet" they are sadly not referring to *our* normal).

    Following Dr. Davis's life-saving advice, I have been wheat-free since last August and avoid grains, and restrict sugar intake. The first time I tested my postprandial glucose after an uncharacteristic meal, I was convinced I had become diabetic. (meal was corn chips, rice, beans, chicken fajitas, and a large margarita). After several consecutive days of eating higher-carb, the same meal generated significantly lower postprandial glucose. (Of course I knew before testing that this meal was a *bad* choice for me).

    Using postprandial glucose levels as Dr. Davis recommends to discover which foods cause your blood glucose to spike (and hence trigger small-dense LDL) is wonderful advice. I have learned that I do not tolerate oat bran! Just be careful not to self-diagnose diabetes based on high readings resulting from uncharacteristic meals. I know Dr. Davis has never recommended this - I only mention it because I really scared myself the first time I measured postprandial sugar, and have since discovered that at least two of my "low-carb" friends had the same experience...

  • zach

    2/5/2010 5:43:05 PM |

    Do you measure one hour after eating?

  • Anonymous

    2/5/2010 5:57:42 PM |

    When you say your patient was at 157 mg/dl postpranial, do you mean right after eating?  Or are you talking about a 2 hour test?  What's the time frame for measuring?  And if you don't do OGTT, how do you control how many grams of carbohydrate you're giving the patient?  Does the load matter?

  • Derek S.

    2/5/2010 7:36:27 PM |

    If coronary risk is increased by 50% at a glucose level of only 126 postprandial, then there is no hope of a heart-healthy diet that takes any form other than Low-Carb or Paleo.  I challenge anyone out there to show me someone who can eat an entire bagel, an apple and coffee (likely sweetened for most people) and maintain postprandial glucose of 100.  Totally impossible.

    Postprandial glucose is not the's the food that's the problem.  The glucose is only the symptom.  Cut out the bagels (and all grains for that matter), fruit (except in small amounts), sugar, processed starch, omega-6 oils while keeping carb intake (via whole foods only) to 20% of calories or less and the postprandial glucose will take care of itself given enough time.

  • davide

    2/6/2010 1:49:01 AM |

    Dr. Davis,

    I'm curious as to whether genetic predisposition plays a factor in how one's body naturally reacts to sugar.

    I happen to have very high LDL cholesterol(220), the vast majority (i think 98%) being very large particles. Yet, I happen to eat a good amount of wheat, juice and fruit, and it doesn't seem to affect my blood sugar or particle size.

    Is this typical with some of your patients?

  • Helen

    2/6/2010 3:28:41 PM |

    Eating low-carb can give you a bigger glucose spike when you do eat more carbs.  (As onschedule noted.)  There may be more than one dietary pattern that keeps blood glucose in a good range for the non-diabetic among us (though I don't think low-fat is it).

    It is possible, as Derek suggested, that the type of carb eaten may be causing some bad change in CVD risk factors (such as grains, sugar, and fruit vs. root vegetables, for instance).  An interesting hypothesis.

  • Jedi

    2/6/2010 5:47:37 PM |

    Derek S I have been checking my fasting and post prandial glucose for a month and i frequently have 100 or less after a carb heavy meal. It is not impossible!

  • ET

    3/16/2010 10:46:23 AM |

    On a low-carb diet, my post-prandial blood glucose level is always 90 or less.

    Several weeks ago, when I donated blood, my blood sugar measured 63 after losing a pint of blood.  Wierd thing is that I felt fine, no shakiness, hunger, or any other symptom of low blood sugar.

    There is a down side to eating low-carb though.  Even a moderate amount of sugar sends my blood sugar through the roof.  My blood pressure increases significantly and I turn beet red and feel awful.  

    I tell my wife that the secret of not eating sugar is to not eat sugar.

  • handsewn

    4/1/2010 1:28:10 PM |

    Thank goodness I found you guys and gals. My daughter has been following a low carb diet to control her type 1 diabetes and she ate a handful of chocolate chips and spiked to 375 almost immediately. I didn't realize that eating low carb can make you super sensitive to carbs. Thank-you for providing this important piece of the puzzle for me!

  • Electronic Medical Records

    5/12/2010 5:26:51 AM |

    Thanks for discussing this...there are so many going through the same situation of ill health and shocking medical reports and not knowing it is common in the world.

  • jignesh

    10/11/2010 7:34:11 AM |

    how to measure after eating...

  • karan

    10/22/2010 6:20:17 PM |

    same question by my how to measure it please reply to it i want to inform this thing to my friend

  • buy jeans

    11/3/2010 7:36:08 PM |

    For this reason, postprandial (not OGTT) glucose checks are becoming an integral part of the Track Your Plaque program. We encourage postprandial blood glucose checks, followed by efforts to reduce postprandial glucose if they are high. More on this in future.

  • Anonymous

    11/17/2010 6:59:41 PM |

    I recently saw an article on veg oil and hexane which eventually led to this blog and others of the same bent, Whole Health Source,, as a result I completely changed my diet. I now eat only meat, whole milk, heavy cream, fresh vegatables, broccoli, spinach, asparagus, salads with balsamic and olive oil, with yams, carrots, or beets once a day for carbs. I eliminated wheat, breads, cerials, sugars, and coffe. Prior to this diet never abused sugar no sodas, occasional ice cream. About a month into this diet I decided to buy a glucose meter and scared myself to serious anxiety as my fasting numbers range from 129-160. The strange thing is that my postprandial numbers if I walk a little after eating range any where from 87-120 usually. and almost never get past 135. Any thoughts?

  • Anonymous

    1/17/2011 4:00:45 PM |

    No one has yet answered the key question - *when* do you measure your one hour and two hour readings? from the start of a meal? End? Mid-way?

    Bloodsugar101 says from the start of a meal, but If you eat and chew slowly - which is sensible - the timing presumably makes BG readings vary quite a lot.

    When I sit down to a meal, it is probably 45minutes from first bite of main course to last bite of fruit/cheese afterward.

  • Anonymous

    1/29/2011 6:38:43 PM |

    Second part of my comment above:

    Also, my resting heart rate came down to 48 bpm. And I plan to get a new lipid profile done soon. My bP was already 120/80, but maybe it has decreased now.

    Pre-diabetes can be reversed with lifestyle modifications. I am not really following a low-carb diet, just a low-calorie, no-junk-food diet. And with only about 45 minutes of exercise on weekdays, it is possible to turn things around.

  • Anonymous

    1/29/2011 6:41:05 PM |

    On Nov 10, 2010, I went for a routine physical checkup while visiting my family in India. I am a lacto-ovo vegatarian. My mother was diagnosed recently with diabetes at 62. I am 40, so I decided to start checking my vitals. My lipids turned out to be (in mg/dL) TC: 170, HDL: 46, LDL: 106; TriGL: 88 and my BMI was 26.2 and resting heart rate 72 beats/minute.

    But my Glucose numbers were not so good:

    Fasting: 98 mg/dL
    2-hr post-prandial OGTT (75g glucose solution): 119 mg/dL

    Since they seemed high, I asked the doctor about this, and he brushed it off saying it was in the normal range of 60-100 for fasting, and less than 145 for the 2-hr test. He also said since the lipid profile was good I should not worry about it.

    An interesting article caught my eye:

    "Extremely short duration high intensity interval training substantially improves insulin action in young healthy males"

    as did the following study by Dr. Christensen:

    I did a lot, and I mean a lot, of online research about nutrition, exercise, types of exercise, caloric restriction, glucose toxicity etc. I must have read at least 200-300 papers and/or articles and 10 different books.

    I used to eat a lot of refined carbs like chips, bagels etc and lots of diet colas (1 can a day). Being a vegetarian, I decided to do things my own way, since none of the existing diets really suited me.  I adopted the following diet and exercise schedule:

    Breakfast: Nutritious Living Hi-lo cereal (low GI low-carb 7g + high protein 12g per serving) along with Soymilk and a sprinkling of walnuts, almonds, pecans, peanuts and chestnuts.

    Lunch: 1 Granola bar (140 cals, 19g carbs) + salad (greens including baby spinach leaves, and vegetables like tomatoes, onions, beans, asparagus, peas, artichokes, beets, brussels, cucumbers, lentils etc) with olive oil dressing + one fruit (orange, pear or apple).

    Snack: 1 fruit and sugar-less black tea.

    Dinner: Two slices of sprouted rye or whole wheat bread, with hummus and some salsa + a few nuts, or mixed vegetable Indian foods (many choices there).

    Water: 2-2.5 liters/day

    Exercise: mornings after getting up and on empty stomach before breakfast, only on weekdays.

    * 15 minute 6.5 mph run on the treadmill to exhaust glycogen stores taking about 225 kCal.

    * 15 minutes weight training with dumbbells (lower-body/upper body on alternate days). Only two sets of 10 reps with medium weights (a pair of 20 or 30 pound dumbbells) in a circuit, making for a vigorous workout.

    * 10 minutes high-intensity interval training on an exercise bicycle. The pattern being, 2 minute warm-up, 6 10-second, extremely intense, all-out sprints at the beginning of each minute, and then a 3 minute cool-down at moderate intensity. At the end of each sprint, my heart-rate would be around 190 bpm, slightly beyond my theoretical max level (220-40 = 180 bpm).

    The result? On Jan 1, 2011, after just 7 weeks of the above routine, my numbers were:

    BMI: 22.6
    Fasting blood glucose: 77 mg/dL
    2-hr post-breakfast (Kellog's raisin bran cereal + nuts + soymilk): 94 mg/dL

    I intend to keep going until I get to:

    BMI: 21.0
    Fasting/2hr-PP: 75/85 mg/dL

  • Anonymous

    1/29/2011 6:42:15 PM |

    Not sure why my two comments above ended up in the reverse order.

  • Anonymous

    2/12/2011 10:56:05 PM |

    To: Anonymous, posting Jan. 29, 2011...
    Very good job w/ changing your #'s via diet / exercise. I've made similar changes, & my numbers are also good. I think the challenge will be ongoing consistency & maintenance.
    Exercise & diet are both huge.

  • vanessa taylor

    8/24/2011 4:29:37 PM |

    Hi, my name is vanessa.  What is normal for blood glucose readings?.  I was told that two hour postprandial was okay as long as it wasn't over 180.  Is this correct?.