The best time to exercise if you have diabetes: Pre-Meal or Post Meal? 

People with diabetes are advised to engage in physical activity. It helps the blood glucose to stay with-in the normal range. It also helps to improve blood circulation, reduce cholesterol, high blood pressure and lower the risk of cardiovascular diseases – complications commonly associated with diabetes.


So, does it really matter if you are exercising after a meal or on an empty stomach? A recent study suggests that it does. According to a research: “post-meal exercise is better than pre-meal exercise for managing hyperglycaemia”. It further suggests that for diabetic patients, the ideal situation should be to use the glucose from the meals rather than triggering the release of glucose from liver.


Why a pre-meal exercise is not a great idea for diabetic patients? To understand the reasons behind this process, let’s start with how does body utilize glucose and most importantly how it maintains the glucose levels with-in a required range.

Blood Glucose or Blood Sugar


Our body converts the food we eat into glucose. It is a form of sugar that makes way into the blood stream. Our cells utilize this glucose to grow and produce energy with the help of insulin, a hormone secreted by pancreas. Insulin helps the glucose to enter the cells. In diabetes, body is:


a) Not able to produce enough insulin (Type 1 Diabetes), or

b) Produces no insulin at all (Type 1 Diabetes), or

c) Does not respond properly to the insulin (Type 2 Diabetes)


Without insulin, there is too much of glucose build-up in bloodstream. Although body gets rid of this excess sugar in the urine, this also means cells are not getting the glucose for energy and growth needs. When the concentration of glucose in blood rises to an abnormal levels, the condition is called hyperglycaemia. It affects both types of diabetes Type I and Type II and also a hallmark for pre-diabetes.


Glucose is not managed by just Insulin: Enters Glucagon


Our pancreas releases another major hormone working in tandem with insulin to maintain the right level of sugar in the body – Glucagon. When we eat, pancreas releases insulin to help lower blood sugar. Between meals or during fasting, we still need energy so pancreas releases glucagon to help keep blood sugar levels steady. How does it all fit together? Let’s find out.


Role of Insulin in maintaining blood glucose:


Insulin is secreted by the beta cells of the pancreas when blood glucose rises, for example, after the meals. It helps to decrease the level of glucose in blood.

  1. Insulin signals the cells – muscle cells, red blood cells and fat cells – to utilize the glucose from the blood to produce energy.
  2. It helps liver and muscles to convert the excess of glucose into glycogen and store it for future, a process called glycogenesis.

As glucose is taken used by the cells and stored in the liver and muscles, its levels in your blood are automatically reduced. And as the levels of glucose falls the blood, the amount of insulin secreted by pancreas decreases. Now kicks in the ‘Glucagon’.


Role of Glucagon in maintaining blood glucose:


Glucagon is secreted by the alpha cells of the pancreas when there is a fall in the level of glucose in blood. Blood glucose is low between meals, during fasting and also during exercise.

  1. Glucagon signals the liver and muscles to break down glycogen into glucose and release glucose back into the blood, a process called glycogenolysis. Glucagon, thus, helps to keep the blood sugar levels from plunging too low.
  2.  It stimulates liver to produce glucose by using other nutrients in the body other than carbohydrates, for example protein. This process is called gluconeogenesis.

 (A quick fact: Many tissues can use other energy sources such as fats or proteins but some organs such as brain and red blood cells can only use glucose.)


Why exercising on an empty stomach can be dangerous in diabetes?


For people who have diabetes, pre-breakfast exercise can actually be harmful and trigger hyperglycaemia, causing the blood sugar to increase. Sounds strange? After all, exercise is supposed to lower blood sugar levels. The key to this mystery lies partly in Dawn phenomenon.


Dawn Phenomenon: Hormonal games our body plays when we are sleeping


In the early morning, at around 3 a.m. and 8 a.m., liver releases certain hormones – growth hormone, cortisol, glucagon, epinephrine – to maintain and nourish the cells of our bodies. These hormones are released when our insulin is wearing out. These counter-regulatory hormones work against insulin’s action, causing the level of glucose in the blood rise. Dawn phenomenon happens to everybody – whether you have diabetes or not. For a person with no diabetes, normal insulin responses help the body to restore the blood glucose to the normal level.


For people with diabetes who do not have enough insulin to regulate the rise in blood glucose, the result is a high glucose reading in the morning. Studies also suggests that when we exercise first thing in the morning before eating anything, we prolong the fasting period which stimulates the release of cortisol, raising glucose even further. Also, let’s see what happens when you are exercising? During exercise the body needs more oxygen especially in the muscles. If you are on an empty stomach, our body is stimulated to release the glucose stored in the liver to meet the high energy requirements. But if there is no insulin or not enough insulin, muscle cells won’t be able to absorb the sugar quickly enough.


Combined result? High level of blood sugar.


(A quick fact: For pregnant women, the dawn phenomenon is even more pronounced as a result of more hormones released in the night.)


How can this be countered?


Data accumulated from many studies and researches show that for people with diabetes 30 minutes after the meal is the ideal time to start exercising. Any physical activity should coincide with the time when the cells have access to the blood glucose coming from the meal.


And how can a meal before exercise help? After the meal, insulin-to-glucagon ratio is high and glucose production from the liver is restricted.  And as the insulin kicks in, the cells starts utilizing the glucose from the blood stream, thereby reducing the blood glucose levels.


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