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Are blood sugar spikes bad?

Are blood sugar spikes bad

The health world has seen a recent shift towards optimizing diet for stable blood sugar. It often means eating low-carbohydrate foods to minimize the rise and fall in blood sugar levels that can be experienced post-meal.

But are blood sugar spikes bad? It’s a question that merits deeper investigation before we start cutting out carbohydrate rich foods that may contain beneficial nutrients.

This article uses a science-backed approach to establish the potential negatives of blood sugar spikes. It also discuss’ what constitutes a ‘spike’, and if changing your diet in the pursuit of complete blood sugar stability is even necessary.

What is a blood sugar spike?

The term ‘blood sugar spike’ refers to a rapid rise and fall in blood sugar that might occur after a meal. It’s usually a consequence of eating a meal that’s high in a type of sugar called ‘glucose’.

During digestion; the meal is broken down and any glucose within the food is deposited into the bloodstream. This is the root cause of a blood sugar spike.

The carbohydrate content of your meal will often have the biggest impact on your post-meal blood sugar spike. Meal timing, metabolic health, sleep and stress levels can also cause an acute rise in blood sugar levels.

High-carb bread

What number is considered a blood sugar spike?

Blood sugar is usually measured in mg/dl. The amount of blood sugar rise that constitutes a ‘spike’ is widely debated amongst health professionals.

There is no exact numerical definition of the term ‘blood sugar spike’ and it can be subjective. Most people will class a rise and fall of 40mg/dl or above as a ‘spike’.

Some ‘influencers’ and ‘experts’ now even view a rise of more than 20mg/dl as a blood sugar spike. Whether this is valid or not is open to interpretation.

Most health regulatory bodies simply suggest that blood sugar levels should be below 140mg/dl 2 hours after eating. Many people in the functional medicine space would say this is too high.

The graph provided below shows a clear example of a blood sugar spike in comparison to a regular ‘healthy’ response.

Blood sugar spike

What triggers blood sugar spikes?


Food is almost always the cause of a blood sugar spike. It’s the natural result of glucose entering the bloodstream following the digestion of carbohydrates and proteins.

The contents of your meal will often dictate whether you have a gentle blood sugar rise or a big spike. High-glucose foods that are rapidly absorbed by the body can cause large amounts of sugar to flood the bloodstream almost instantaneously.

The most common foods that cause a big blood sugar spike are refined carbohydrates. White rice, white bread, pasta, candy, cakes, cookies and pastries are all examples of foods that are extremely high in rapidly digesting glucose. Each of these foods have also been stripped of their fiber and nutrients during processing.

It’s worth noting that protein has a marginal impact of blood sugar, while fat will not cause any rise at all. Pairing your carbohydrate rich foods with fiber, fat or protein can slow down digestion and ultimately blunt the blood sugar response.

High glucose food

Insulin resistance

Insulin is a hormone that works to shuttle sugar out of the bloodstream and into your cells. The pancreas will secrete large amounts of insulin to cope with the incoming blood sugar following a high-carbohydrate meal.

Most people that continuously overeat processed carbohydrates will inevitably become insulin resistant. It’s a state in which your cells become resistant to the impact of insulin and refuse to accept more sugar into the cells.

Once the cells start refusing to absorb blood sugar, it is often left circulating in the blood stream for much longer than expected. This can cause a spike in blood sugar and may ultimately lead to type 2 diabetes if left untreated.

Other lifestyle factors

A variety of lifestyle factors can cause a sudden blood sugar spike. This is often due to the liver dumping sugar into the bloodstream under times of ‘stress’.

Some common events that could cause a blood sugar spike:

  • Intense exercise
  • Upon waking up in the morning (aka ‘dawn phenomenon’)
  • Acute dehydration
  • Coffee (for some people, not all!)
  • Artificial sweeteners
  • Sudden stress (e.g. giving a presentation)
Person exercising

How long do blood sugar spikes last?

The timing and duration of a blood sugar spike depends on the food you have eaten and your individual tolerance to carbohydrates. It can vary from meal to meal, person to person and day to day.

Most people will see their blood sugar peak at around 1 hour post-meal. If the meal is high in fiber, protein and fat; you can expect this peak to arrive later. If your meal only consists of refined carbohydrates; the spike may arrive sooner.

Individuals with fully functioning blood sugar control should see levels come back down to baseline within 2-3 hours. The rate at which blood sugar returns to normal is dependent on your personal physiology.

Exercising before or after a meal can also shorten the duration of a blood sugar spike. Sleep, stress management and gut microbiome status may also play a role, along with many other factors.

Walking after a blood sugar spike

Is it bad for your blood sugar to spike?

The simple answer is: Yes.

Blood sugar spikes can cause acute damage to various organs and have a negative impact on your circulatory system. You will likely run into health issues if you consistently consume food that cause extreme rises and falls in blood glucose levels.

One excellent review published in 2018 gave us a good summary of the many issues that can arise due to consistent blood sugar spikes. It cited diabetes, heart disease, obesity and accelerated aging as key problems one may encounter in the long-term.

In the short-term, excessively high blood sugar can also lead to headaches and increased thirst. Following an acute spike, blood sugar will often rapidly crash down to a level even lower than before the meal. This often leads to feelings of intense hunger ( or ‘hanger’), shakiness, lightheadedness and fatigue.

The constant ups and downs associated with spikes is often referred to as the ‘blood sugar rollercoaster’. It’s a ride that is largely caused by eating the standard western diet of refined sugar, flour, starch and oil.

blood sugar crash

Why are blood sugar spikes bad?

Heart disease

One interesting study published in 2009 hypothesized that blood sugar spikes “induce endothelial dysfunction, inflammatory reactions and oxidative stress”. Each of these reactions are strongly correlated with cardiovascular events and coronary heart disease.

Another study published in 2004 also pointed out the strong correlation between post-meal blood sugar levels and heart disease. It theorized that a spike in glucose has a toxic effect on the vasculature and could damage the inner walls of veins and arteries.

The conclusion of a 2006 study advised that post-meal blood sugar spikes ‘should be considered a cardiovascular risk factor…it should be monitored and treated’.

It’s clear that blood sugar spikes are strongly linked to heart disease. In fact, it appears that having intermittent spikes may actually be worse than chronically raised blood sugar in relation to heart disease risk.

heart disease

Type 2 diabetes

Type 2 diabetes is arguably the most obvious disease that may result from blood sugar spikes. It’s a disease in which the cells become resistant to effects of insulin trying to move sugar out of the blood stream, leading to chronically raised blood sugar levels.

The pancreas is tasked with producing a hormone called insulin that transports sugar out of the blood and into the cells. When blood sugar is spiked to supernatural levels it can put significant strain on the pancreas.

This constant overworking of the pancreas can inhibit its ability to produce insulin after a number of years. Once this happens, fasting and post-meal blood sugar levels will typically rise into the diabetic range. Type 2 diabetes is then diagnosed at this stage.

Insulin resistance of the cells can also happen simultaneously throughout this process. The constantly spiked levels of insulin will essentially make the cells refuse to store any more sugar. This causes post-meal spikes to be even bigger while the body struggles to find somewhere to store the sugar.

It’s this potent combination of pancreas failure and insulin resistance that leads to type 2 diabetes. It’s a progressive disease that will lead to a myriad of health problems unless diet and lifestyle are addressed.



The link between glucose spikes and cancer has been largely overlooked by modern medicine. However, a long-term study of Japanese patients in 2019 found a strong link between elevated post-meal blood sugar levels and cancer mortality.

A range of additional studies have also shown that post-meal glucose spikes are “implicated in the development of cancer”. This includes a 2007 prospective study that followed over 64,000 people in northern Sweden and measured cancer risk in relation to post-meal blood sugar. It concluded that blood sugar spikes are associated with total cancer risk in men and women.

Further research looking into the mechanism by which blood sugar spikes increase cancer risk still needs be conducted. However, the current data already shows an incredibly strong correlation that cannot be ignored.



Blood sugar spikes can be a direct cause obesity. The acute rise in blood sugar levels following a high carbohydrate meal stimulates large amounts of insulin production that can lead to weight gain.

The above mechanism is due to the ‘storage signal’ that is sent out by insulin. It tells the body that we’re in a time of food abundance and blocks its ability to burn fat. In essence, it tells your body to store all the fuel during this feast before there is a famine.

Consistently spiking blood sugar will lead to chronically and acutely elevated levels of insulin (known as hyperinsulinemia). This ensures the body is constantly in storage mode and is reluctant to liberate stored body fat.

Having regular blood sugar and insulin spikes can also lead to insulin resistance. This means the cells have become reluctant to store the blood sugar being carried by insulin and has been independently shown to cause weight gain.

A blood sugar spike generally happens when you’ve put too much rapidly digesting energy into the body . It’s more energy than the body can use in that moment so it must be stored as fat for later use. This is the concept of ‘calories in, calories out’.


Cognitive decline

A 2006 study concluded that exaggerated post-meal blood sugar spikes “are associated with a derangement of both global, executive, and attention functioning”. It also noted that reducing blood sugar spikes may prevent cognitive decline.

The above study points to the fact that mental health is strongly tied to blood sugar metabolism. In fact, the brain uses glucose as its primary fuel source and nutritionally induced…brain insulin resistance may lead to cognitive decline. Blood sugar spikes are one of the main causes of insulin resistance.

Another study has also discovered that post-meal blood sugar spikes are associated with white matter hypertensity; which is a key predictor of stroke, dementia and death. The same study also found atrophy (shrinkage) in the brain following an acute rise in blood glucose.

The evidence showing that blood sugar spikes may cause cognitive decline is overwhelming. It shouldn’t be too surprising given the brain’s need for a steady and reliable fuel source.

Further health issues related to blood sugar spikes

  • Inflammation
  • Lack of focus
  • Fatigue
  • Frequent urination
  • Increased thirst
  • Headache
Cognitive decline

Can you have blood sugar spikes and not be diabetic?

Absolutely. Many people without diagnosed diabetes will see their blood sugar spike in certain situations.

Eating a significant amount of refined carbohydrates can be enough for those with a healthy metabolism to see an acute rise in blood sugar. Sugar sweetened beverages and candy are often the worst offenders. These hyper-processed, glucose rich ‘food like products’ will usually spike blood sugar regardless of your health status.

Statistics published by the American Diabetes Association in 2019 also estimated that 8.5 million Americans are currently living with undiagnosed diabetes. The same survey also found that 96 million Americans are suffering with prediabetes and the majority of these cases are likely undiagnosed.

Another alarming study published in 2019 concluded that only 12% of Americans are metabolically healthy. This means the majority of the population will have issues with blood sugar control despite not being formally diagnosed with a disorder.

We know that eating ultra-processed carbohydrates (candy, cakes, cookies, etc.) and lack of physical activity can lead to glucose spikes in healthy people. However, these spikes may be even more pronounced in most individuals given the general state of poor health at a population level.

Carbohydrate rich donut

What can I do if my blood sugar spikes?

The fastest way for diabetic patients to reduce blood sugar is by injecting fast acting insulin. Alternatively, exercise is the most effective lifestyle intervention for non-diabetics.

Performing physical activity will increase your body’s demand for energy and force it to burn the glucose in your muscle cells. Burning off your stored energy will create more storage space for the sugar that’s circulating in the bloodstream.

Exercise has also been shown to to increase glucose uptake without the need for excess insulin. It’s an effect that can see a dramatic reduction in blood sugar levels during and after a muscle-stimulating workout.

The impact of exercise is more than just short-term. Consistently moving your body throughout the day can also improve overall insulin sensitivity to reduce the risk of future blood sugar spikes.

Running after a blood sugar spike

How to avoid spiking blood sugar

  • Eat whole, unprocessed foods.
  • Don’t eat refined carbohydrates.
  • Lower your overall sugar intake.
  • Eat fewer total carbohydrates.
  • Balance your meals with fiber, fat and protein
  • Exercise regularly. Especially before and after mealtime.
  • Drink enough water.
  • Get 7-9 hours sleep per night.
  • Manage stress levels.
Healthy blood sugar food


Are blood sugar spikes bad? Yes.

Spiking blood sugar to super physiological levels can be detrimental to your energy levels and wellbeing in the short-term. It can also cause a cascade of physical health conditions if it happens consistently for a number of years.

Focusing on eating healthy whole-foods, performing regular exercise and getting enough sleep should keep your glucose in the normal range.

If you do have a ‘cheat meal’ that spikes your blood sugar; don’t beat yourself up. Once in a while is not much of a problem, but multiple times per day can cause serious issues.

Having stable blood sugar is the result of making generally healthful choices. Don’t get hung up on the details, just keep making the right dietary decision, most of the time.

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