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I always felt that exercise before breakfast was a great way to burn fat (especially abdominal fat). A fasted state from overnight of not eating after dinner means that once the stored carbohydrate is used up, the body has to get into the fat source to give the required energy for energy.

It seems that researchers at the University of Bath and University of Birmingham also thought to look into this.

What they did…

So they took men who were overweight or obese and put them into two groups. The first group of 12 men did moderate intensity cycling before breakfast. Then they did the same exercise another day but after eating a mixed meal breakfast.

The second group of 30 men did the exercise before they had any carbohydrate and after they had carbohydrate. Their exercise period was for 6 weeks.

The researchers measured how the muscles used the fat and also how sensitive the body was to insulin. Insulin is released after glucose is ingested.

A little bit of background here. Being obese and sedentary causes the skeletal muscle to reduce insulin sensitivity. So when the muscles are not as sensitive to insulin, they cannot use the circulating glucose and the insulin builds up in the blood (called hyperinsulinemia). Hyperinsulinemia increases risk of cardiovascular disease. Regular exercise increases insulin sensitivity and reduces insulin building up in the blood after a meal (known as postprandial insulinaemia).

Blood samples and breath tests were taken. Also samples of skeletal muscle from the thigh of the men.

What they found… Exercise before breakfast is better than after breakfast.

Their findings were as followed:

• Exercise before nutrient ingestion (breakfast or glucose ingestion) increased the whole body and skeletal use of fat.
• When breakfast or glucose was given, the whole metabolism of the body changed. The body used the glucose and decreased the use of fat.
• Exercise before ingesting the glucose increased the use of fat (fat was used around 2 times more than with exercise before compared to after carbohydrate ingestion).
• Exercise training before eating carbohydrate increased insulin sensitivity.

My reflection on this research:

Here are some thoughts from me regarding this research.

1. If you have existing conditions such as heart disease or diabetes, then exercising in fasted state is not a good thing. You may actually put yourself at risk of hypoglycemia (low blood sugar).
2. The men in these studies were overweight or obese. The results may be different for those who are lean as a lean muscle may have a different metabolism pathway. In those who are lean and in absence of stored fat, the next source of energy is protein in muscle so I do have a caution about this practice for those who are lean. We really want to conserve the muscle protein when we exercise.
3. If someone is overweight / obese and sedentary, then exercising before breakfast may be a good way to utilize the stored fat and also improve the insulin sensitivity.
4. This study did not show weight loss in the period of 6 weeks but did show improvement in insulin sensitivity and fitness level of those who participated. A longer study will be useful to see if exercising before breakfast for those who are obese or overweight impacts weight loss efforts and makes them more leaner than those who have exercise after breakfast.
5. This research only used men. So research on women’s response to exercising before breakfast needs to be looked at.

For me, I will continue to do my exercise before having breakfast. Only because it fits my household routine.

Reference:

Edinburgh R et al. Lipid metabolism links nutrient – exercise timing to insulin sensitivity in men classified as overweight or obese.

https://academic.oup.com/jcem/advance-article/doi/10.1210/clinem/dgz104/5599745

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