For many people exercise reduces that feeling of hunger we call ‘appetite’. This is due to a decrease in ‘ghrelin’ levels in the brain while also increasing leptin concentration. To understand this process better we must first look at what these hormones do in the body…
What is Ghrelin?
Ghrelin is a hormone produced by the stomach. It is released mainly from the stomach, but can also be released in small amounts from the brain, pancreas and small intestine. Although ghrelin serves many functions in the body, one of its main functions is to increase appetite and stimulate the release of growth hormone. It also promotes fat storage.
What is Leptin?
Leptin is a hormone fat cells secrete to help regulate body weight. It signals to the brain’s ‘hypothalamus’ and works by altering food intake, as well as controlling calorie burn in the long term. Its effects are exaggerated when you lose weight and leptin levels fall.
When levels fall, it stimulates appetite to increase food intake as a way to ensure we maintain a normal weight. It also throws some light on the reason people who are trying to lose weight often struggle to lose those last few pounds (many of us have been here!).
Exercise temporarily decreases your appetite, however the length of time you will feel this effect depends on a number of factors such as the type of exercise, duration of training and intensity of the workout.
Exercise Reduces Appetite For Some….
Let’s evaluate some of the research findings: In regards to intensity of the workout,
short and/or low intensity exercise may suppress hunger, but it’s more likely to happen with longer and/or more intense exercise. This is likely due to the fact that the duration or intensity of the workout was not enough to get the same hormonal or blood shift effects.
A study published by the journal of endocrinology found running for shorter durations at a higher intensity (36 minutes at 75% maximum heart rate) affected ghrelin levels more than running for longer periods at a lower intensity (55 minutes at 50% maximum heart rate).
Some research suggests the type of exercise you do can impact appetite changes. A study in the American journal of physiology suggested that a 60 minute run can cause ghrelin levels to drop, and peptide YY (a gut hormone that suppresses appetite) to rise. A 90 minute strength session also lowered ghrelin levels but did not affect peptide YY.
Temperature may also play a vital role. When you workout intensely and for a long duration you will get hot, and when you are really hot you are not hungry. Often you may not feel hungry again until your body cools down.
During your workout it is likely you won’t feel hungry as blood gets diverted away from your stomach to power your working muscles. The fact digestion slows when exercising means feelings of nausea and acts of vomiting during exercise is not uncommon. It’s hard to be hungry when your feeling nauseated.
A study funded by the national institutes of health and presented by the endocrine society found that exercise only reduced appetite in lean women. For the obese women that participated, there was no reduction in leptin during high intensity exercise as was seen in the lean participants. They were only able to reduce leptin levels during moderately intense exercise. The research suggests obesity interferes with leptin appetite suppressing abilities and the detection of exercise energy expenditure.
A small study of 33 men conducted in 2013, and published in Metabolism, showed that while aerobic and resistance training decreases fat mass, the rate of perceived fullness was higher after aerobic exercise. Aerobic activities such as running suppress the appetite more than lifting weights or other forms of resistance training.
If Your Goal is Weight Loss or Performance:
It is important to refuel after a workout. If you are trying to build muscle or improve performance getting nutrients in after training is key for progress. You need protein for recovery and repair and carbohydrates to replenish glycogen stores. If you skip this, you may feel sluggish with decreased performance abilities. If your not hungry, a protein shake blended with fruit such as berries and almond milk may be a good choice.
If your hoping to use exercises appetite suppressing abilities to eat fewer calories and lose weight faster you should rethink your approach. Often after the suppression of hunger wears off, your going to feel ravenous making you less inclined to make smart food choices. Smoked salmon with eggs or grilled meat /fish with leafy greens after training will replenish your body with the macronutrients it needs, keeping you fuller for longer and able to make smart food decisions for your next meal.
It is also important to not choose your exercise based on how well it suppresses your appetite. It’s better to include both cardio and strength exercises since they have different benefits, and to choose exercise you enjoy and are likely to do long term as part of a healthy lifestyle.
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