Joslin's Diabetes Deskbook, Updated 2nd Ed., Excerpt #24: Physical ...

?Introduction

Exercise is probably one of the earliest treatments for diabetes. It was noted in writings of ancient physicians and it has remained, along with diet, weight management and the use of insulin, an important part of the treatment troika. In recent years, the benefits of fitness derived from a physically active lifestyle have been extolled for everyone, not just those with diabetes. The result has been a renewed interest in this component of diabetes management as a primary focus of treatment, rather than merely as an action in the daily routine for which compensatory adjustments in food, insulin and other antidiabetic medications are necessary.

A physically active lifestyle has multiple fitness and health benefits for people with and without diabetes, including:

• reduction of cardiovascular risk
• improved lipid profile
  • decreased triglycerides
  • increased high-density cholesterol
• improvements in mild to moderate hypertension
• increased energy expenditure, promoting
  • weight reduction and weight management
  • preservation of lean body mass
• increased strength and flexibility
  • enhanced bone density
  • improved posture and balance
  • decreased risk of falls and injuries
• increased ease of daily activities
• improved sense of well-being

For people who do have diabetes, the impact of a physically active lifestyle can extend beyond the usual issues of fitness, because it may:

• lower blood glucose concentrations
• reduce glycohemoglobin levels (A1C)
• reduce the dose of oral diabetes medications and/or insulin needed
• increase the chance that the diabetes can be managed without any pharmacologic intervention
• increase insulin sensitivity
• reduce hyperinsulinemia

People with diabetes have a two to four times greater incidence of cardiovascular disease (CVD) compared to age and gender matched people without diabetes, and CVD is responsible for approximately 75% of diabetes-related deaths. A fitness regimen is an important tool in reducing these statistics. Its effects in improving insulin sensitivity and glucose control, combined with the benefits of cardiovascular training and resulting reductions in lipids and hypertension, clearly have significant implications for macrovascular health. For the person with diabetes or prediabetes, a program of regular physical activity impacts glucose metabolism not only by directly lowering the blood glucose levels, but also by improving the body's sensitivity to the effects of insulin. Indeed, it has recently been suggested that a fitness regimen, including weight reduction, can reduce the occurrence of type 2 diabetes. Two major studies, The Finnish Diabetes Prevention Study and The Diabetes Prevention Program (DPP) found that people at high risk for developing type 2 diabetes can lower their chances of getting the disease by as much as 58% by modest, sustained weight loss (10-15 pounds) and about 30 minutes of moderate intensity physical activity each day.

Effects of Physical Activity on People without Diabetes

When people are at rest, circulating free fatty acids provide up to 90% of the needed fuel for the skeletal muscle. Physical exertion, however, significantly increases energy requirements, which can come from a number of sources. Fat stored in muscle and free fatty acids released into the circulation from adipose tissue are two major sources. In addition, normal exercising muscle rapidly increases glucose utilization, which is obtained through the breakdown of glycogen stores in muscle and liver and the uptake of glucose from the circulation. During physical exertion insulin levels drop, while levels of counterregulatory hormone such as epinephrine, glucagon, and cortisol will rise. These hormone shifts result in further increases in blood levels of glucose and free fatty acids that can be used for energy, and reduce the risk of hypoglycemia.

The fuel for short bursts of physical exertion is primarily glucose. Muscle glycogen is used initially, followed after about two to three minutes by glucose from the circulating blood. After about 15 minutes of activity, however, the glucose used for fuel and maintaining adequate blood glucose levels comes increasingly from glucose newly made in the liver from glycogen breakdown or through gluconeogenesis. Blood glucose levels may actually rise in this circumstance, as glucose production may be greater than glucose utilization. Some energy can also be provided by the breakdown of protein into amino acids and their direct metabolism, or conversion, into glucose in the liver (especially alanine).

After about 30 minutes of physical exertion, as glycogen stores in liver and muscle start to become depleted, new production of glucose (gluconeogenesis) increasingly begins to supply glucose needs. However, such glucose production often cannot keep up with needs. To provide for these needs, and also to prevent overutilization of glucose and resulting hypoglycemia, the body turns to the free fatty acids for more of its energy supply.

Exercise results in increased insulin sensitivity, leading to increased glucose uptake by muscle cells during the post-exercise period. This effect may be seen for as long as twelve hours, and in some cases as long as twenty-four hours, after the physical activity has been completed, and is related to the rebuilding of the glycogen stores in the muscle and liver.

This phenomenon is commonly referred to as the "lag effect." Insulin must be available for this process to occur, but there also must be enough glucose in the blood from which to make the glycogen. In people with diabetes, if the blood glucose levels are too low after physical exertion or there is too much insulin, the rebuilding of the glycogen stores can result in hypoglycemic reactions over the next several hours.

Effect of Physical Activity on People with Diabetes

Type 1 Diabetes

The ability of someone with type 1 diabetes to compensate for physical exertion is determined by the amount of available insulin, the degree of diabetes control, and the state of hydration. In theory, and often in reality, the person with well-controlled diabetes with insulin and food/fuel in proper balance can handle activity just as well as someone without diabetes. However, if the control is poor and the balance of these components is not well established, physical exertion can trigger significant metabolic aberrations.

In a person with poorly controlled diabetes, there is increased glucose production by the liver, as well as increased release of fat from adipose cells. This occurs as the deficient levels of insulin result in even higher blood glucose levels during physical exertion, with excessive hepatic glucose production adding to the problem.

The metabolism of free fatty acids results in the increased production of ketones. Thus, exercise by a person with poorly controlled type 1 diabetes results in elevated levels of glucose, as well as rising levels of ketones from the utilization of free fatty acids as an alternative fuel.

There is another interesting change that occurs with physical exertion in people with diabetes. As long as the diabetes is well-controlled and sufficient insulin is present, the additional glucose needed to fuel increased activity does not require an incremental amount of insulin. Muscle contraction itself increases glucose uptake by muscle fibers. As a result, more glucose utilization can occur per unit of insulin by working muscle than by resting muscle. For these reasons, physical activity is one of the three major factors affecting blood glucose levels, along with food and insulin.

Type 2 Diabetes

Exercise or physical exertion by a person with type 2 diabetes usually leads to a reduction in blood glucose levels. This is particularly so for people with type 2 diabetes who are in the hyperinsulinemic phase of the disease, as physical exertion does not induce as much of an insulin reduction as it would in someone without diabetes. Physical exertion increases insulin sensitivity, and as insulin resistance is a hallmark of type 2 diabetes, physical exertion directly works counter to the pathophysiologic abnormality causing this condition to occur. In fact, if those with type 2 diabetes are treated with oral antidiabetic medications or insulin, symptomatic hypoglycemia may develop. They may also demonstrate a significant lag effect, with the hypoglycemic effect persisting or occurring a number of hours after the activity has occurred.

The most striking benefit of an improved fitness level for the patient with type 2 diabetes is the increase in insulin sensitivity that can result. It is well known that lack of physical exertion can lead to some impairment in glucose tolerance, even in a person who does not have diabetes. Many people with type 2 diabetes are sedentary and this certainly contributes to their insulin resistance. By contrast, when such people participate in some form of endurance training or physical fitness program, they can experience improvements in insulin sensitivity. Even very obese individuals will improve glucose metabolism in response to a regular physical activity program. People with type 2 diabetes undergoing physical fitness training can demonstrate reductions in both fasting and postprandial glucose values, benefits not generally seen in people with type 1 diabetes.

Next Joslin Excerpt: Chapter 6 Physical Activity for Fitness - The Physical Fitness Program

Copyright ? 2010 by Joslin Diabetes Center. All rights reserved. Reprinted with permission. Neither this book nor any part thereof may be reproduced or distributed in any form or by any means without permission in writing from Joslin.?Note: Joslin does not endorse products or services.

You can purchase the updated 2^nd?Edition of JOSLIN'S DIABETES DESKBOOK at:

https://www.joslin.org/jstore/books_for_healthcare_professionals.html

Please Note: Reasonable measures have been taken to ensure the accuracy of the information presented herein. However, drug information may change at any time and without notice and all readers are cautioned to consult the manufacturer's packaging inserts before prescribing medication. Joslin Diabetes Center cannot ensure the safety or efficacy of any product described in this book.

Professionals must use their own professional medical judgment, training and experience and should not rely solely on the information provided in this book to make recommendations to patients with regard to nutrition or exercise or to prescribe medications.

This book is not intended to encourage the treatment of illness, disease or any other medical problem by the layperson. Any application of the recommendations set forth in the following pages is at the reader's discretion and sole risk. Laypersons are strongly advised to consult a physician or other healthcare professional before altering or undertaking any exercise or nutritional program or before taking any medication referred to in this book.

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Source: http://www.diabetesincontrol.com/index.php?option=com_content&task=view&id=14059&Itemid=5

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