Morning vs Afternoon Exercise Debate: A False Dichotomy

Michael Riddell, PhD


August 17, 2023

Should we be exercising in the morning or afternoon? Before a meal or after a meal?

Popular media outlets, researchers, and clinicians seem to love these debates. I hate them. For me, it's a false dichotomy. A false dichotomy is when people argue two sides as if only one option exists. A winner must be crowned, and a loser exists. But in reality, a gray zone exists, and/or a number of options are available. For me, exercise at any point of the day is a win.

Michael C. Riddell

Some but not all research suggests that morning fasted exercise may be the best time of day and condition to work out for weight control and training adaptations. Morning exercise may be a bit better for logistical reasons if you like to get up early. Some of us are indeed early chronotypes who rise early, get as much done as we can, including all our fitness and work-related activities, and then head to bed early (for me that is about 10 PM). Getting an early morning workout seems to fit with our schedules as morning larks.

But if you are a late-day chronotype, early exercise may not be in sync with your low morning energy levels or your preference for leisure-time activities later in the day. And lots of people with diabetes prefer to eat and then exercise. Late chronotypes are less physically active in general compared with early chronotypes, and those who train in the morning tend to have better training adherence and expend more energy overall throughout the day. According to Dr Normand Boulé from the University of Alberta, who presented on the topic of exercise time of day at the recent American Diabetes Association (ADA) Scientific Sessions in San Diego, morning exercise in the fasted state tends to be associated with higher rates of fat oxidation, better weight control, and better skeletal muscle adaptations over time compared with exercise performed later in the day. Dr Boulé also proposed that fasted exercise might be superior for training adaptations and long-term glycemia if you have type 2 diabetes.

But the argument for morning-only exercise falls short when we look specifically at post-meal glycemia, according to Dr Jenna Gillen from the University of Toronto, who debated Boulé at the recent ADA Scientific Sessions debate, also in San Diego, and also publishes on the topic. She pointed out that mild- to moderate-intensity exercising done soon after meals typically results in less glucose spikes after meals in people with diabetes, and her argument is supported by at least one recent meta-analyses where post-meal walking was best for improving glycemia in those with prediabetes and type 2 diabetes.

The notion that post-meal or afternoon exercise is best for people with type 2 diabetes is also supported by a recent reexamination of the original Look AHEAD Trial of over 2400 adults with type 2 diabetes, wherein the role of lifestyle intervention on cardiovascular outcomes was the original goal. In this recent secondary analysis of the Look AHEAD Trial, those most active in the afternoon (between 1:43 PM and 5:00 PM) had the greatest improvements in their overall glucose control after 1 year of the intensive lifestyle intervention compared with exercise at other times of day. Afternoon exercisers were also more likely to have complete "remission" of their diabetes, as defined by no longer needing any glucose-lowering agents to control their glucose levels. But this was not a study that was designed for determining whether exercise time of day matters on glycemia because the participants were not randomly assigned to a set time of day for their activity, and glycemic control was not the primary endpoint (cardiovascular events were).

But hold on a minute. I said this was a false dichotomy argument. It is. Just because it may or may not be "better" for your glucose to exercise in the morning vs afternoon, if you have diabetes, it doesn't mean you have to choose one or the other. You could choose neither (okay, that's bad), both, or you could alternate between the two. For me this argument is like saying; "There only one time of day to save money"; "to tell a joke"; "to eat a meal" (okay, that's another useless debate); or "do my laundry" (my mother once told me it's technically cheaper after 6 PM!).

I live with diabetes, and I take insulin. I like how morning exercise in the form of a run with my dog wakes me up, set me up for the day with positive thoughts, help generate lots of creative ideas, and perhaps more importantly for me, it tends not to result in hypoglycemia because my insulin on board is lowest then.

Exercise later in the day is tricky when taking insulin because it tends to result in a higher insulin "potency effect" with prandial insulins. However, I still like midday activity and late-day exercise. For example, taking an activity break after lunch blunts the rise in my glucose and breaks up my prolonged sitting time in the office. After-dinner exercise allows me to spend a little more time with my wife, dog, or friends outdoors as the hot summer day begins to cool off. On Monday nights, I play basketball because that's the only time we can book the gymnasium and that may not end until 9:45 PM (15 minutes before I want to go to bed; if you remember, I am a lark). That can result in two frustrating things related to my diabetes: It can cause an immediate rise in my glucose because of a competitive stress response and then a drop in my glucose overnight when I'm sleeping. But I still do it. I know that the training I'm doing at any point of the day will benefit me in lots of little ways, and I think we all need to take as many opportunities to be physically active as we possibly can. My kids and I coin this our daily "fitness opportunities," and it does not matter to me if its morning, noon, or night!

It's time to make the headlines and arguments stop. There is no wrong time of day to exercise. At least not in my opinion.

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