Biochemically speaking, caloric restriction and aerobic exercise are the worst ways to burn fat. Practically speaking, they’re also the only ways. So what does one do with this conundrum? I’ll qualify my opening statement, and then provide the best solutions.
When essentially any organism (even the little microscopic guys squirming around you all day) restricts its calories, whether by choice or (in the case of pretty much anything but a well-to-do human) due to environmental constraints, a multitude of mechanisms are in place to preserve their survival. Reduced access to any essential macronutrient (carbohydrates, fats, proteins) or micronutrient (vitamins, minerals) will result in the inhibition of their use, activation of their uptake/storage and preservation. That is, take away food, and the food that is left will be absorbed and stored more voraciously, and used much more judiciously.
Additionally, when an organism requires the production of more energy for various reasons (e.g. increased periods of wakefulness; cardiovascularly demanding work), certain unessential processes will be discontinued/limited, and the upregulation of energy-producing machines (mitochondria, for those who remember their biology a bit) will follow. That is, aerobic demand will teach your cells to more efficiently produce and utilize energy. We don’t want that! That means the same exercise routine you did a week ago is now going to burn much less fat, today.
What should you – the human animal – who restricts their caloric intake or engages in aerobically demanding exercise, do? Start by. This is the number of calories your body is expected to require to maintain its current weight, if you were to simply sleep all day long. When you begin a plan to cut weight, you should absolutely maintain at least this number of calories. There are a variety of other calculators available online which will also estimate the additional calorie intake you require, based on your general activity level. I recommend you begin your plan by eating your calculated daily calorie needs and create the deficit through exercise. Furthermore, I recommend you have your daily calories come from 40% protein/35% carbohydrates/25%fat (remember that, while protein/carbs = 4cal/gram, fat = 9cal/gram). This resolves the problem of eating too few calories. Your body will initially recognize that it’s getting as much energy as it requires. Therefore, it will not immediately go into alert-mode, learning to utilize less calories. What about the exercise problem?
(HIIT) is one of the best solutions to the exercise problem. In it’s most basic form, this could mean 15 minutes on the treadmill: a series of 1-2 minute intervals of alternating moderate-level and very intense-level running. More creative and intense implementations are recognized in the link I’ve provided, and are essentially circuit training. The beauty of HIIT is that your body will not adapt to the high-level stimulus (at least, not as quickly). That is, the intervals of moderate activity establish the baseline activity your system expects to need to maintain. The intense intervals (and these should be an 8 or 9 on a scale of 1-10; 10 being, you feel like you’ll die if you go a second longer than the interval time) burn the bulk of the calories in a short period of time. Furthermore, this method of periodicity has been shown to increase your metabolism for up to 24 hours following HIIT. That is, the caloric deficit problem is even better addressed because your body is stimulated to consume more energy than it generally would, at rest.
I recommend you begin your plan with 10-15 minutes of HIIT (with a proper ~2 minute warm-up), five times a week. Resist the urge to trudge through an hour-long session of moderate jogging. 15 minutes of HIIT will come close to burning the same number of calories and, in the long run, prevent your body from becoming a highly efficient machine for prolonged exercise. Rather, it will promote your muscles’ development into efficient, high-intensity burst-producing machines. Compare a marathon runner’s body to a sprinter’s; which aesthetic are you after? Unless you’re training for a marathon, I’m guessing the end-goal is the sprinter.
As your training continues, the inevitable issues for which I first presented my case will rear their ugly heads. Despite your best intentions and execution of the principles I’ve laid out, your body will adapt to fewer calories and increased exercise. So, depending on how long you intend to continue a cutting routine, you will have to compete in this arms race against your own apparatus. When you hit a plateau (no measurable loss of fat for 1-2 weeks), reduce your calories by 300 as a male, or 150-200 as a female. Generally, it is best if all of these calories come from carbohydrates, but never allow their consumption to get below 1/2 gram a day, per lb of body weight. You can also increase your number of cardio sessions, increase their duration (no longer than 25 minutes of HIIT, per session), vary their type (e.g. eliptical; weight circuit training), or increase their intensity.
Finally, as you reach a good stopping point or you reach a final plateau, it is important to slowly re-introduce your calories/carbohydrates (+300 calories a week for a male; +150-200 as a female) until you return to maintenance or higher consumption. It is a good idea to increase your cardio a bit during this adjustment time to prevent your body from “bouncing back” and storing too much of the new calorie bounty. Then, taper your cardio back to a reasonable level, over time, when you are back on a maintenance-level of calories.
About Author: Alex Bradley, Avid amateur bodybuilder “hobbyist” for 8 years; PhD student in biochemistry