Is Interval Training the Magic Bullet for Fat Loss?
August 08 2019
This was a recent study that made some headlines looking at at the optimal mode of cardiovascular exercise to lose fat. If you think you need to lose some fat, check this out.
What was the study about?
They compared two modes of cardio: Interval training vs continuous training using a study design called a meta-analysis.
Meta-analysis: Instead of a single study, a met-analysis is simply a collection of previously conducted studies to make one large study. Generally, the conclusion drawn from a ‘well-done’ meta-analysis is more believable or credible than a single study. The simple logic is that the chances of one study being wrong are high, but that of multiple studies being wrong are low.
Interval training: The meta-analysis looked at studies which compared interval training to regular continuous training. So what is interval training? Interval training involves bursts of high-intensity work alternated with active rest intervals. For example, running for few minutes paired with walking. A few types of interval training are:
- High- Intensity Interval Training (HIIT): When the intensity is high (near maximal)
- Moderate Intensity: When the intensity is moderate.
- Sprint Interval training: Involves all out sprinting (maximal effort)
Continuous Training: This is the traditional form of cardio that most people are used to in which we run or cycle continuously at a moderate intensity for 45-60 minutes.
What studies did they include?
Briefly, the meta-analysis included only studies in English, were at least 4 weeks in duration. had interval training or sprint interval training compared with moderate intensity continuous training, and had measures of body fat.
What were conclusions?
After the inclusion and exclusion criteria, 36 studies were selected for analysis. The conclusions from the abstract:
- Interval training and continuous training both reduce body fat percentage (%).
- Interval training provided 28.5% greater reductions in total absolute fat mass (kg) than continuous training.
My Comments:
Most people who read the abstract jump to the conclusion that interval training is the way to go. However, here are a few points that might make you rethink your conclusion:
28.5% reduction in fat: As they conclude, the interval training group lost 28.5% fat mass than continuous training. Sound impressive, isn’t it? But how much fat loss are we talking about. 28.5% means 0.45 kg of fat! Guess what, it doesn’t sound that impressive now. The lesson here is beware of impressive percentage reductions or increases; it may not mean much.
Interval training & time: Arguably the major benefit of interval training is that it is time efficient. So how much difference did they see in time? The average duration for Interval training was 28 min and that for continuous training was 38 min. So you save just 10 minutes! I saving 10 min worth the discomfort and risk of injuries?
Adverse effects: One of the negative effects of interval training is the fatigue and injuries that comes along. They mentioned it, but did not evaluate it quantitatively. Adverse effects are very important when we are talking about high-intensity training (researchers take note pls). Unfortunately, most exercise studies do not report adverse effects in a systematic manner. It s also important to consider that most people do both strength training and cardio whereas in the studies they only performed cardio. So the fatigue will be lot higher than if you are performing interval training and weight training.
8-12 weeks studies: What is abundantly clear after decades of weight loss research is that losing weight is easy, keeping it off is THE real challenge. It reminds of the that famous quote by Lincoln, “It’s Easy to Quit Smoking. I’ve Done It a Thousand Times”. If people are aware of this fact, there would be less number of diets and less number of folks arguing about the best diet. And all these 6-12 week studies are just examples of weight “loss” and says zilch about weight maintenance, which is the real problem. And weight maintenance requires lot more than just exercise!
Exercise & weight loss: One of the major reasons exercise is recommended for weight loss is to reduce the loss of muscle that happens with weight loss. Calorie restriction, and not exercise, is the primary strategy for weight loss. Unfortunately, this study did not look at muscle mass. Considering the higher intensity, interval training may have maintained greater muscle mass which is important (maybe more important than fat loss).
Study quality: What was the quality of the studies? The quality of the studies was low. They did not mention it in the abstract, but when the study quality is low, take the results with a grain of salt.
Exercise benefits: Finally, now there is more and more research showing that exercise has number of beneficial effects that is independent of weight loss. So even if you are not losing weight, you are still reaping a number of neurological, psychological, metabolic and cardiovascular benefits that no pill can claim. Please do think about those when you exercise.
Could you give some tips and examples for interval training?
Of course. Based on research studies:
- Have a base aerobic fitness before you jump on HIT. So continuous training for a few weeks before you start
- A 5 min warm up and few minutes of cool down
- Choose stationary cycle or elliptical. Avoid running on treadmills for safety
- Most studies had them perform 3 times/week
- Gradually progress out intensity
Commonly used interval training protocols:
So what should I do to lose weight & keep it off?
I would say the three things that you should focus if losing fat and keeping it off is your goal:
- Calorie restriction (or diet as they say)
- Physical activity or exercise (cardio & strength training)
- Behavioral approaches to improve adherence: Most people talk endlessly about the above two, and will completely miss the 3rd one. Unless you make behavioral changes to stick to your new dietary and activity patterns, you WILL gain most it back. Almost all weight loss recommendations include behavioral strategies. And almost everyone who has successfully kept weight off has knowingly or unknowingly made behavioral changes.
Conclusions
- Looking at the amount of fat loss, the study quality, time taken, and other above factors, I wouldn’t make any strong recommendation for either of the exercise modalities. Pick the one you enjoy the most and that you can continue for years.
- If fat loss (and keeping it off) is your goal, focus on calorie restriction & exercise and, more importantly, on behavioral stratergies so that you can stick with the above.
- If you are looking for a magic bullet for fat loss as the title claims, I have news for you: there isn’t one. 😊
