How different amounts of walking influence fat burning and metabolic responses to a high-fat meal Original paper

In this randomized controlled trial, walking 5,000 steps or more during a single day increased fat oxidation compared to walking only 2,000 steps, and walking 10,000 steps during a single day improved the metabolic response to a high-fat pizza meal.

The effect of daily step count on postprandial (postmeal) metabolism in response to a high-fat meal.

11 young adults (average age of 30; 5 women and 6 men) without any known health conditions.

On average, participants had a daily step count of approximately 7,700 per day.

In this randomized controlled crossover study, the participants completed 4 conditions, each separated by a 3-day to 10-day washout period.

All conditions involved the consumption of a high-fat mixed meal (HFMM), a frozen pizza containing 960 calories, 36% carbohydrate, and 48% fat.

Before the meal, the participants completed 1 of 4 “doses” of daily steps in a single day: 2,000, 5,000, 10,000, and 15,000. Daily steps were completed in 3 approximately equal bouts throughout the day (e.g., for 10,000 steps, the participants would complete 3 bouts of about 3,333 steps). Steps were taken at a cadence of 100 steps per minute. The HFMM was consumed 2 hours after the final walking bout.

Before the HFMM and every 30 minutes after for 4 hours, blood samples were obtained from the participants to measure triglycerides, blood glucose, low-density lipoprotein cholesterol, high-density lipoprotein cholesterol, nonesterified fatty acids, and insulin. In addition, the researchers assessed resting energy expenditure, fat oxidation, and carbohydrate oxidation in each condition approximately 1 hour after the last bout of walking and before the HFMM. Hunger and palatability were assessed before and after consumption of the HFMM.

Triglycerides were lower after the HFMM in the 10,000-step condition compared to the 2,000-step condition. NEFAs were higher in the 15,000-step condition compared to both the 2,000-step condition and (nonsignificantly, p=0.078) compared to the 10,000-step condition.

Although energy expenditure, carbohydrate oxidation, and fat oxidation were not different between conditions, subgroup analyses accounting for sex indicated that fat oxidation was greater in the 5,000-step, 10,000-step, and 15,000-step conditions compared to the 2,000-step condition, an effect driven by male participants.

Fat oxidation rates with different steps per day

The origins of 10,000 steps as a public health recommendation can be traced back to a Japanese marketing campaign for a pedometer (a step counter) called “Manpo-kei”, which translates to “10,000 steps meter.” Dr. Yoshiro Hatano, a Japanese researcher and professor of health and welfare, used this marketing to encourage people to become more physically active and burn more calories, which he thought would help prevent obesity and other health issues related to a sedentary lifestyle.

Despite its historical — rather than evidence-based — origins, numerous studies have provided support for the benefits of 10,000 steps. The risk for all-cause mortality, cardiovascular disease mortality, and cancer mortality are reduced with daily step counts up to, beyond, and sometimes even below 10,000 per day.^[1][2][3] This research was covered in detail in an Editor’s Pick from March 2022.

Because walking is such an easy and accessible form of physical activity and because steps are a simple way to prescribe physical activity, finding the optimal dose of walking that yields health benefits is a worthwhile endeavor.

Postprandial lipemia (PPL) and postprandial glycemia (PPG) refer to the acute elevation in blood lipids (e.g., triglycerides) and glucose, respectively, following a meal. Both processes have been demonstrated to play a role in the development of atherosclerosis.^[4][5] Specifically for PPL, the mechanism appears to involve endothelial (dys)function, inflammation, and oxidative stress.^[5]

Furthermore, elevated PPL and PPG have been associated with a greater risk of cardiovascular disease (CVD), even more so than fasting levels of triglycerides and glucose.^[6][7][8]

Exercise has beneficial effects on reducing PPL^[9] and PPG^[5], and a few variables have been suggested to modulate the effects of exercise/physical activity on PPL and PPG.

A negative energy balance may be one crucial factor. Replacing the calories “lost” during exercise abolishes the beneficial metabolic effects on PPL.^[10][11][12] Replacing the exercise-induced energy deficit with carbohydrates, but not fat or protein, also diminishes the improvements in insulin sensitivity and glycemic control at ensuing meals, possibly by refilling depleted muscle glycogen stores.^[13][14] In other words, to have beneficial postprandial effects, exercise must result in an energy deficit.

In the current study, the energy intake of the participants was similar on all of the experimental days — approximately 2,200 calories — but energy expenditure was, by design, different. On average, the participants in the 2,000-step condition were in a positive 382-calorie surplus, whereas in the 15,000-step condition, the participants were in a 234-calorie energy deficit. Energy balance for the 5,000-step and 10,000- step conditions were slightly positive and neutral, respectively.

Despite the negative energy balance incurred in the 15,000-step condition, there was no “metabolic benefit” associated with taking more steps. This might be explained by the fact that the pizza meal, which contained approximately 960 calories, would have put all participants into a positive energy balance, thereby diminishing any benefits of exercise on PPL or PPG after the meal. The energy deficit theory also doesn’t explain the improved PPL in the 10,000-step condition, in which there was no energy deficit.

Exercise intensity may also explain the lack of a benefit of exercise on PPL (in conditions other than the 10,000-step condition) and PPG. Research indicates that higher-intensity exercise may result in a more robust improvement in PPG compared to moderate-intensity exercise.^[15] When different volumes of exercise are matched for intensity, as in this study, the effect on PPL appears to be the same.^[16] The intensity was 100 steps per minute in all conditions, equivalent to 3 metabolic equivalent tasks (METs) or moderate-intensity exercise. Perhaps exercise intensity was just too low.

What could explain why 15,000 steps didn’t improve PPL to a similar or greater extent than 10,000 steps?

The authors speculate that the acute rise in NEFAs played a role. It’s possible that the greater activity levels in this condition increased neurally stimulated lipolysis and/or resulted in an increase in the activity of lipoprotein lipase, the enzyme responsible for promoting the release of free fatty acids into the bloodstream. NEFAs transiently induce insulin resistance^[17] and increase glucose levels and hepatic triglyceride output,^[18] which could abolish any PPL-lowering and PPG-lowering effects of exercise.

These results support the goal of 10,000 steps per day as an evidence-based recommendation for improving metabolic health. Although it’s unclear whether more than 10,000 steps are better, it’s probably a good idea to add more walking to your day.

Stringent dietary and lifestyle controls were implemented in this study, which helps to isolate the effects of the step count manipulation on the metabolic outcomes. For example, the participants’ physical activity levels were consistent in the days leading up to each experimental condition, and their step counts were nearly identical on each preexperimental day. Furthermore, the participants consumed a similar diet on each preexperimental day and ate standardized meals during each condition. This increases the likelihood that the differences observed between conditions were due to the step counts, not some external variable.