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Blood Glucose Explained

Updated: Jan 17, 2021


Why is your doctor asking you to be so strict regarding your carbohydrate and sugar consumption? Does eating a little bit really matter that much?


The truth is that if you are diabetic, pre-diabetic, or are insulin resistant, YES, it matters.


Blood glucose levels fluctuate as a person’s intake of food varies throughout the day. After meals, the body is in an “absorptive state” and is absorbing nutrients from the gut. During the absorptive state, blood glucose levels rise as your body absorbs carbohydrates and proteins (fats do not cause an increase in blood glucose). While this process is buffered to an extent by the liver, which stores glucose, this is a normal physiological process.


When digestion is complete and the absorption of nutrients decreases, the body is in a “post-absorptive state.” At this point, the body’s cells begin to use glucose to make energy and blood glucose levels fall.


Normal blood sugar represents less than one teaspoon of sugar dissolved in the blood. This may rise slightly with food consumption, but should quickly return to normal within one hour. A healthy blood glucose number to have throughout the day is 80 mg/dL (+/- 5).


If you are skeptical of this claim, let me walk you through it.


One liter (L) = 10 deciliters (dL)

One gram (g) = 1000 milligrams (mg)

One teaspoon = 5 grams (g)


We know that on average a human body has about 5 L of blood in it. The question is, how much sugar dissolved into that 5 L of blood gives us a reading of 80 mg/dL?


Because 1 liter equals 10 deciliters we multiply 80 mg/dL by 10, which give us 800 mg, the amount of sugar in 1 liter. Multiply the 800 mg in 1 liter by 5 liters (the number of liters in the human body) and we get 4000 mg of sugar. If we divide 4000 by 1000 (the number of milligrams in a gram) we get 4 grams of sugar, approximately 4/5 teaspoon. This measurement, 4/5th teaspoon of sugar, is all you need to have in your blood stream in order to complete all your energy needs in one day.


While most guidelines, including the American Diabetes Association, recommend the fasting blood sugar of a pre-diabetic be set between 100 – 125 mg/dL and anything over 125 mg/dL is considered diabetic, you should question this recommendation and do your own math.


Without walking you through the calculations, here are some calculations of how much sugar is in x mg/dL:


99 mg/dL = 4.95 g (remember 5g = 1 teaspoon)

126 mg/dL = 1 ¼ teaspoons

140 mg/dL = 1 ½ teaspoons

200 mg/dL = 2 teaspoons (double the healthy amount)


As you can tell, the difference between having a healthy blood glucose and a diabetic blood glucose is about one quarter of a teaspoon. Imagine what happens if you drink a soda with 10 teaspoons of sugar in it!




When we have healthy control over our blood glucose our body is able to bring that spike you will see with any carbohydrate or sugar down to normal levels relatively quickly. As we lose control of this process, by poor dietary choices, lack of exercise, genetics, poor sleep, stress, and many other environmental factors we do not yet understand, we develop insulin resistance which leads to type two diabetes. If you are a type one diabetic patient, you deal with this battle every day.


To answer the question we started with, does eating a little bit or cheating here and there really matter? As you can see it really does matter. Increasing your blood glucose by adding just a tablespoon can further damage your metabolic health. Working with a doctor who understands the complexity of this process and how to better control your blood sugar using diet is imperative.


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