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Home » Exercise timing may have an effect on obesity and type 2 diabetes

Exercise timing may have an effect on obesity and type 2 diabetes


New research shows that the time of day for exercise may have different effects on obesity and type 2 diabetes. Over the years, I have heard different anecdotes and claims made about exercise, but I dismissed them since there was no real data to support these claims. Some studies have shown that there are links between exercise and various health issues, but the data is not overwhelming.

I think these recent studies can help physicians and others involved in treating both obesity and type 2 diabetes (which are often linked) give better advice to their patients.

As I usually do, I will review this study with you, giving you a summary of the results and a critique of the quality of the research.

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Photo by Nataliya Vaitkevich on Pexels.com

Diabetes – the short version

Just for background, type 2 diabetes mellitus (or type 2 diabetes, T2DM) is a metabolic disorder that is characterized by high blood glucose with insulin resistance and relative insulin deficiency. In general, someone with T2DM produces low (or maybe even adequate) insulin levels, but various cells and organs become resistant to insulin, so cells don’t remove the glucose or store it.

Although the cause of T2DM is not completely understood, it results from a complex interaction between diet, obesity, genetics, age, and gender. Some of the causes of T2DM are under a person’s control, like diet and obesity, but many of the causal factors are not.

Because they are often confused, it’s important to note that T2DM has a completely different etiology and pathophysiology compared to type 1 diabetes mellitus (T1DM, once called juvenile diabetes). Type 1 diabetes results from the inability of the beta cells of the pancreas to produce insulin, as a result of an autoimmune disease. Diet and lifestyle are not related to T1DM.

There are numerous medical treatments and lifestyle changes that can moderate, or even reverse, the course of T2DM. On the other hand, there are no cures (at this time) for T1DM, and it can be a death sentence for the patient without regular daily insulin injections. However, over 90-95% of diabetes cases in the USA are Type 2.

The consequences of both types of diabetes are almost the same. Complications of poorly managed diabetes mellitus may include cardiovascular or heart diseasediabetic nerve problems, and diabetic eye problems, among many other chronic conditions. 

Exercise, type 2 diabetes, and obesity papers

In a paper published on 4 September 2023 in the journal Obesity, Tongyu Ma, PhD, research assistant professor with the Health Sciences Department, Franklin Pierce University, Rindge, NH, and colleagues studied data on almost 5300 individuals, finding a strong association between moderate to vigorous physical activity (MVPA) and reduced obesity.

The key finding for this paper was that people who exercised in the morning had a lower body mass index than those who exercised at other times, even though they were more sedentary. The research cannot tell us why morning exercise is better, but the study authors speculated that morning exercise raised the basal metabolic rate is raised early in the day which could burn more calories.

Here are some of the key results:

  • Individuals who exercised in the morning had a lower body mass index (BMI) than those who exercised at other times of day. The morning group had a BMI of 27.4, compared to 28.4 for those who exercised at midday and 28.2 for the evening.
  • Morning exercisers also had a lower waist circumference than participants. The morning group averaged 95.9 cm compared to 97.9 cm and 97.3 cm for the midday and evening groups, respectively.

These researchers stated that “although a beneficial association among the levels of physical activity with obesity has been frequently reported, the optimal timing of physical activity for decreasing obesity remains controversial.”

In the second paper published on 20 September 2023 in the journal Diabetologia, Chirag J. Patel, Ph.D., associate professor of biomedical informatics at Harvard Medical School, Boston, MA, and colleagues examined more than 93,000 individuals in the UK Biobank database. They found that morning and afternoon, but not evening, exercise reduced the risk for type 2 diabetes.

However, the researchers also indicated that people who undertook at least MVPA were protected against developing type 2 diabetes no matter what time of day they exercised. The researchers suggested that it would be “helpful to include some higher intensity activity to help reduce the risk of developing diabetes and other cardiovascular disease.”

The key results of this study were:

  • After adjustment for potential confounding factors, both morning and afternoon physical activity were associated with a 10% and 9% reduced risk, respectively.
  • However, there was no association between evening activity and the risk for type 2 diabetes.

Summary

I believe that there are three key takeaways from both papers:

  1. Moderate to vigorous physical activity is important to reduce obesity no matter the time of day.
  2. Moderate to vigorous physical activity during the morning provides more benefits to controlling obesity.
  3. Morning and afternoon physical activity reduced the risk of type 2 diabetes.

I believe that based on the size of these studies plus the quality of the statistical analysis, these two studies seem to provide evidence that you should exercise in the morning, though any vigorous exercise at any time of the day is probably beneficial for reducing obesity and the risk of type 2 diabetes.

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Michael Simpson

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