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Sugar Surfing Lesson #10: Why does my blood sugar change unpredictably?

Whenever I’m asked about why someone’s blood sugars seem so unpredictable and hard to control, I just envision some of the possible reasons why and how this can happen. The reasons for this variance are NUMEROUS. Most of them are not mutually exclusive. In fact, when you consider the number of possible combinations of 1 or more of the reasons listed below, the number is too staggering to calculate. Many of these possible explanations are either unknown or underappreciated. Some are fortunately rare.

Sugar Surfing™ assumes that our blood sugar levels are in constant motion. I call it “flux and drift”. In 2008, I said The only person with a straight-line blood sugar is a dead person”. If you review some of the list of possibilities below, you might even add a few I’ve left out.

The teaching point is simple: glycemic variance is baked into all of us. Many of these variables can be learned and effectively managed using Dynamic Diabetes Management methods (Sugar Surfing). Others can only be responded to ‘in the moment” when they happen or are discovered. Sugar Surfing is always part proactive, part reactive.

Next time you find yourself perplexed by an unexpected change in blood sugar (either up or down), pull up this list and consider some of the possible reasons. As your surfing skills improve and mature, this list will start to become intuitive. Some of these are very uncommon. You will ultimately develop your own list of "usual suspects" and develop effective tactics to counteract them. Reading the book Sugar Surfing and/or reviewing previous posts on this page are your best first step resources.

This list IS NOT all inclusive, but it's a start. Hopefully, your view of the "glycemic universe" just got a little bigger!

Factors with the potential to impact blood sugar control which good Sugar Surfers should be aware of:


Insulin type (rapid, fast, intermediate, long acting) and action

Amount of insulin taken

If on pump: normal bolus, extended bolus or combination bolus

If on pump: use of temporary basal rates

Injection/infusion site on body or route (injected, pump or inhaled)

Injection into fatty areas (lipohypertrophy slows insulin absorption)

Insulin antibodies (can bind and delay insulin action)

Kidney function (reduced kidney function = prolonged insulin activity)

State of insulin (partially disintegrated due to heat or freezing)

Factors which influence absorption of insulin from site (hydration status, exercise)

Frequency of dosing (overlapping effects of one or more insulins types; stacking)

Timing of insulin dose relative to the meal or snack eaten

Use of insulin for correcting out of range blood sugars (under dosing, overdosing, use of fixed dose corrections)

Insulin pumps (multiple basal rates, wrong times on pump, air bubbles in tubing, tunneling at the site, dislodged site, improperly inserted site, degraded insulin from prolonged reservoir use, programming errors)

Failure to inject or bolus (omission)

Wrong dose or bolus given (errors)

Surreptitious insulin dosing

Failure to increase insulin dosing in response to stress of illness


Composition of the food consumed (carbs [simple/complex], fat, protein, fiber)

Meal frequency/overeating (intentionally and unintentionally)

Snacking frequency (amount and type)

Order in which food during a meal is eaten

How thoroughly food is chewed

Completeness of cooking of the food

Hidden nutritive (caloric) additives in foods/snacks

Poor carb counting/No carb counting

Impact of fat and protein on digestion

Impact of various sugars (sucrose, fructose, lactose, etc.…)


Duration of exercise, intensity of exercise

Injecting during exercise or into an exercising extremity

Aerobic vs anaerobic exercise

Post-exercise hypoglycemia (hours after exercise; glycogen depletion from liver)

Stress hyperglycemia during exercise

Eating during exercise

Stress and Illness

Infection (viral, bacterial, fungal) (localized or systemic)


Psychological stress (may raise or lower BG)

Depression (may raise or lower BG)

Anxiety (may raise or lower BG)


BG Meter errors and normal meter variance

Poor blood sugar measuring technique

Sensor error and/or mis-calibration

Interfering substances


Alcohol (impairs ability to raise BG when low: gluconeogenesis, may impair judgment)

Mixed drinks (some may have carbs, may impair judgment)

Tobacco (may reduce appetite)

Caffeine (may reduce appetite)


Steroids [glucocorticoids] (type, route, duration, amount, frequency) will increase glucose production and insulin resistance.

Stimulants (may decrease appetite)

Many other medications exist with variable effects on BG levels or judgment of user


Bowel disease/Celiac disease (treated or untreated) (reduced absorption of carbohydrates from gut)

Hypothyroidism (untreated) may raise BG due to lower metabolic rate

Hyperthyroidism (untreated) may lower BG due to higher metabolic rate

Many other diseases could impact BG up or down (too numerous to list)

General health

Regular vs infrequent exercise (affects insulin response)

Rate of stomach emptying (varies some from day to day)

Residual insulin production ability (may vary from day to day)

Quality of existing glycemic control (influences insulin action, e.g., glucose toxicity)

Trending direction and rate of change of BG level when insulin, food and/or exercise are done

State of hydration

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