Does Cardio Make You Fat?

Does Cardio Make You Fat?

Some people say that cardio will make you fat.

This is not true. Cardio does not directly cause you to gain fat. You gain body fat when the energy that is entering the body is greater than the energy that is leaving the body.

There are certain situations in which doing cardio exercise along with other behaviors can increase the likelihood that someone will gain body fat. But it is very important that everyone understand that cardio is not directly causing this to occur.

It is true that in this article we wrote, “aerobic exercise is a fat trap.” It is completely reasonable that the average reader could interpret this to mean that aerobic exercise—which is generally what people mean when they talk about “cardio”—makes you fat.

For the sake of preventing further confusion, let us clarify the statement with points from the literature:

  • We know from a 2011 review by Boutcher that "the effect of regular aerobic exercise on body fat is negligible." Sprint intervals work better.
  • Over the long-term, cardio leads to the loss of lean muscle mass, which reduces the amount of calories burned by the body at rest (Westcott, 2009). If one doesn’t reduce calorie intake at the same rate, fat gain occurs.
  • According to a 2009 review by Boutcher, short-term aerobic exercise studies designed to reduce body fat are “disappointing” because they produce less than expected fat loss.
  • A 1997 meta-analysis by Miller of 493 studies showed that changing diet is a much more effective way to reduce body fat than doing cardio in overweight people.
  • The purpose of aerobic exercise is to train the body to be as efficient as possible. The body adapts quickly to repetitive aerobic exercise with the goal of using the least amount of oxygen and energy to perform the greatest amount of work. This does not promote fat loss.

See this effect in action with Williams’ 2006 survey of 12,568 runners in which only those who increased their weekly distance or running speed over the 9-year study did not gain fat. Those who maintained or slightly increased mileage and intensity had larger waistlines by the end of the study.

All this evidence is just the tip of the iceberg indicating that cardio is not a very useful form of exercise for losing body fat. It begs the question:

Why do some people gain fat even though they do cardio, and how can this be avoided?

The following ten rules will answer this question and help you to experience all of those good things that can come out of exercise: a perfect body composition, boundless energy, and a workout program you don’t need to stress about.

#1: Aerobic-style cardio is most effective if you are overweight and new to exercise. A number of things relevant to fat loss occur when you first start doing cardio:

  • You burn calories during the workout and during the post-workout recovery period.
  • Your body increases its ability to burn body fat and to switch between fat burning and carb burning—an adaptation that is highly beneficial for fat loss.
  • Insulin sensitivity improves and your body uses the sugar in the blood more effectively.

Depending on the intensity and length of workouts (75 percent of maximal heart rate for 40 minutes is often used in studies), you can expect to lose 1 to 2 kg of fat in 3 to 4 months, assuming you don’t change your diet.

A review of studies reported that cardio interventions of at least 15 weeks led to about 1.5 kg of fat loss, and lean people tend to lose less fat than overweight folks.

#2: Eventually, the body adapts and uses energy and oxygen more efficiently during cardio, making it less effective for fat loss. Workouts will feel easier and if you want to continue experiencing the same metabolic benefit, you have to either increase intensity and train faster, or increase the distance.

For example, scientists estimate from calorie balance equations that it would require upwards of 1 hour of moderate-intensity cardio 7 days a week to produce continual fat loss to the tune of about 1 pound a week in active individuals.

Even this enormous volume of exercise will lead to diminishing returns in the long run because muscle mass will be lost. Plus, the repetitive exercise stress could lead to altered hormone balance. Further, calorie balance equations do not prove to be very applicable to real life situations.

#3: Too much cardio can lead to increased hunger and food intake, which leads to fat gain. Not only do people often eat more when doing cardio, misconceptions about how to “fuel” exercise have led people to eat high-glycemic foods before, during, and after exercise, which suppresses fat burning.

Light and moderate intensity cardio such as walking, jogging, or a bike ride won’t significantly deplete energy stores or cause muscle damage, and extra protein or carbs aren’t necessary and may negate a calorie deficit. Plus, both cause the release of insulin, which is not ideal when the goal is fat loss.

There’s even evidence that some people reward themselves for exercising by eating carbohydrate-dense, high-fat foods, which leads to fat gain.

#4: Doing cardio to lose fat in conjunction with calorie restriction leads to weight cycling. People initially lose fat and muscle. Then when they increase calories and stop dieting, they gain the fat back. They also replace the lean muscle that was lost with fat.

This is a worse body composition, which means their body will burn fewer calories at rest, and it increases disease risk. For example, people who do cardio with repeated diets in the hopes of losing fat have more inflammation and a higher risk of heart disease than people who don’t diet or exercise and remain the same weight.

#5: People with elevated cortisol from chronic stress are less likely to lose body fat from cardio because high cortisol causes the body to store fat. Here’s what happens when cortisol is high all the time:

  • Cells become resistant to insulin, causing inflammation, and making body unable to access body fat to burn for energy.
  • The hormones that regulate hunger can become imbalanced. Compared to people with normal cortisol, people who suffer more stress and have high cortisol have 15 percent higher ghrelin, which triggers hunger, and 15 percent lower leptin, which suppresses hunger.
  • High cortisol makes people favor high-sugar foods to replace the neurotransmitter serotonin, which is depleted during chronic stress.
  • Growth hormone (GH) and testosterone (T) are suppressed, which is associated with fat gain, particularly in the belly and trunk area.

Therefore, a few things are indicated if you have high cortisol and want to reduce body fat. First, you have to adopt stress reduction methods (focusing on sleep, supplementation, meditation, fun activities).

Second, fix your diet by choosing lower glycemic, whole foods. Third, try strength training instead of cardio as your main exercise mode because it can help to balance cortisol with other hormones like GH and T, while improving insulin sensitivity.

#6: High cortisol combined with cardio produces changes in the body making fat gain more likely. The simple act of doing cardio can increase cortisol.

In normal circumstances this is not a problem and the cortisol release will be transient. Remember, healthy, sedentary people who start to do cardio will improve insulin sensitivity and fat burning. They are likely to lose some fat as well.

But, combine the cortisol spike from daily cardio with an elevated cortisol curve due to stress, and you have a fat trap. This is most likely to happen with higher intensity or longer duration cardio workouts. Also, fasted, intense training can cause elevated cortisol, whereas going for a walk, or other casual exercise is less likely to be a problem.

The bottom line is that you could end up gaining fat even though you do cardio if you have high cortisol because you might end up eating more than you intend or being less physically active so you burn fewer calories over the course of the day.

#7: Anecdotal reports suggest women tend to have a greater difficulty losing body fat from cardio than men over the long-term. A few things make this more likely to happen:

We’ve already established that if you experience weight cycling from calorie restriction and cardio, you’ll progressively reduce muscle mass and have a lower metabolic rate. Women are especially susceptible because they start out with lower muscle mass to begin with.

Women may be at a greater risk of experiencing elevated cortisol in response to repetitive training stress because hormone balance may be more delicate. High cortisol from excessive training stress will cause a woman’s body to shuttle the hormone pregnenolone into cortisol production instead of using it to make progesterone, which is a hormone that facilitates the use of fat for energy.

In turn, this reduces estrogen and testosterone, which need to be balanced for optimal metabolic health in women.

#8: Cardio interferes with muscle building. This is a well-known fact in sports science:

When endurance athletes lift weights, they get stronger and increase the size of the Type II muscle fibers, but they rarely gain muscle mass. They will often lose body fat as well with the addition of strength training, which produces a much more favorable body composition for endurance performance.

A recent study illustrates this. Researchers had both young untrained men (Strength group) and a group of elite cyclists (Cyclists) do a strength training program. The Strength group did no cardio and the Cyclists did their regular aerobic training.

The Strength group gained about 1 kg of muscle, whereas the Cyclists gained zero. In addition, the Strength group increased quad and hamstring cross-sectional area by 50 percent more than the Cyclists.

Scientists believe aerobic type cardio "turns off" muscle building pathways and promotes catabolism, inhibiting muscle development. It’s also possible that the high volume of exercise required from both cardio and lifting workouts led to elevated cortisol, further impairing muscle growth.

Therefore, if you’re trying to build muscle, which is absolutely the best plan for reducing body fat and keeping it off, don’t do steady-state cardio.

#9: Interval training is more likely to produce fat loss than cardio, and it will allow you to save training time because it builds lean muscle mass.

An abundance of studies show that the many versions of high-intensity training, such as sprints, circuit training, strongman, and even more moderate intervals are all better choices for fat loss than steady-state cardio for the following reasons:

  • You burn more calories in less time. Depending on how hard you push during the intervals, you can burn more calories in just 25 minutes than you can in double that time when doing cardio.
  • You experience a more robust energy expenditure in the 24-hour post-workout recovery period than with cardio because your body requires a lot of extra energy to restore metabolic balance and remove waste products.
  • Genes involved in protein synthesis (muscle building) are turned on and you will be more likely to experience a better hormonal environment post-workout, with an elevation in GH and testosterone along with cortisol. This allows interval training to sustain lean muscle mass and may even build muscle for a better metabolic rate.
#10: Strength training is a superior form of exercise that will allow you to be satisfied with your physique.

It optimizes lean muscle mass, elevates metabolic rate, and improves insulin sensitivity. It also improves hormone balance, reduces inflammation, and supports cardiovascular health.

Take Away Points:
  • Prioritize diet, lifting, and stress management if your goal is fat loss. Add in some form of intervals to accelerate results. The optimal intensity for your intervals will vary based on individual factors such as stress levels, carb intake, gender, age, training background, and so forth.
  • If your only goal is to build muscle, avoid cardio completely. Focus on putting your energy into lifting and strongman workouts. Prioritize diet and recovery.
  • If you are passionate about endurance exercise but need to lose fat, replace some of your steady-state cardio workouts with moderate-intensity intervals. Add strength training to your activities.
  • If you are training for an endurance race and want to improve performance, do a strength-type lifting program with heavy loads (80 percent of the 1RM or heavier) in order to optimize body composition.
  • If you are a power athlete, avoid cardio because power is the performance variable that is MOST compromised by steady-state cardio—much more than strength or hypertrophy.


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