Chapter 21:
Effects of exercise on ketosis
Simply restricting carbohydrates will establish ketonuria (presence of ketones in the urine)
given enough time (typically 3-4 days). The requirements for the establishment of ketosis are
discussed in detail in chapter 4 but are briefly reviewed here. Additionally, exercise interacts with
carbohydrate restriction and affects ketosis. This chapter discusses the role of exercise, both in
helping to establish ketosis, as well as its impact on ketosis once established.
A recap of ketogenesis
Ketosis requires a shift in the liver away from triglyceride synthesis and towards free fatty
acid (FFA) oxidation and ketone body formation. Blood glucose must also drop, lowering insulin
and increasing glucagon and decreasing the I/G ratio. Along with this hormonal shift, there must
be adequate FFA present for the liver to produce ketones.
Exercise is inherently ketogenic and all forms of exercise will increase the rate at which the
liver releases its glycogen, helping to establish ketosis. As the rapid establishment of ketosis is
important for individuals using the CKD approach (who only have 5-6 days to maximize their
time in ketosis), strategies for entering ketosis are discussed. The overall effects of exercise on
ketone concentrations is also discussed.
Section 1: Aerobic exercise
It has been known for almost a century that ketones appear in higher concentrations in
the blood following aerobic exercise (1). During aerobic exercise, liver glycogen decreases, insulin
decreases, glucagon increases and there is an increase in FFA levels in the bloodstream. During
aerobic exercise, there is a slight increase in blood glucose uptake which peaks around ten
minutes. To maintain blood glucose, the liver will increase liver glycogen breakdown, keeping
blood glucose stable for several hours.
Thus, the overall effect of aerobic exercise is to increase the production of ketone bodies
(2,3). The increase in ketone bodies during exercise is smaller in trained versus untrained
individuals, due to decreased FFA mobilization during exercise (2).
Aerobic exercise can quickly induce ketosis following an overnight fast. One hour at 65% of
maximum heart rate causes a large increase in ketone body levels. However, ketones do not
contribute to energy production to any significant degree (4). Two hours of exercise at 65% of
maximum heart rate will raise ketone levels to 3mM after three hours. High levels of ketonemia
(similar to those seen in prolonged fasting) can be achieved five hours post-exercise (4). This
increase in ketone bodies post exercise allows for glycogen replenishment in the muscle. Since