By Dr. Mercola
A common assumption about exercise is that it will motivate you to eat more. But recent research turns this assumption on its head by showing that 45 minutes of moderate-to-vigorous exercise in the morning may actually reduce your food cravings.1
The study included 18 women of normal-weight, and 17 who were clinically obese. Their neural activity in response to images of food was measured on a morning following exercise, and on a morning when they did not exercise.
Images of flowers were used as a control. Perhaps surprisingly, they discovered that the women's attentional responses to images of food decreased after a brisk walk on the treadmill.
"This study provides evidence that exercise not only affects energy output, but it also may affect how people respond to food cues... We wanted to see if obesity influenced food motivation, but it didn't. However, it was clear that the exercise bout was playing a role in their neural responses to the pictures of food."
In both groups of women, morning exercise also resulted in an increase in total physical activity that day, and, perhaps more importantly, they did not compensate for the energy expenditure by eating more later in the day.
According to the authors, further research is needed to determine whether or not the diminished motivation for food persists long-term if you exercise regularly. I would counter that by pointing out that the evidence supporting exercise for normalizing your weight and approach to food is so overwhelming, you really don't need to wait for such results... Exercising first thing in the morning, especially if done on an empty stomach, has been shown to be particularly beneficial. Your choice of breakfast food may also play a significant role in decreasing or heightening sensations of hunger afterward.
Why Eating Breakfast Might Increase Hunger
The interesting aspect about eating first thing in the morning is that it coincides with your circadian cortisol peak, that is, the time of day when your cortisol (stress hormone) levels rise and reach their peak. The circadian cortisol peak impacts your insulin secretion in such a way that when you eat during this time, it leads to a large and rapid insulin release and a corresponding rapid drop in blood sugar levels, more so than when you eat at other times of the day.
If you're healthy, your blood sugar levels won't drop to a dangerously low level (such as what can occur with hypoglycemia) but they can drop low enough to make you feel hungry. This is more commonly experienced in people who are not insulin resistant (such as those who are overweight or have type 2 diabetes), but rather are lean and "insulin sensitive." Because the circadian cortisol peak adds another insulin-boosting effect on top of an already insulin-sensitive individual, the low blood sugar and subsequent hunger may therefore be more pronounced.
It's also important to realize that eating a full meal, particularly carbohydrates, will inhibit the sympathetic nervous system (SNS) and reduce the fat burning effect of your exercise. Instead, eating lots of carbs activates your parasympathetic nervous system (PSNS), which promotes energy storage – the complete opposite of what you're aiming for.
Although conventional wisdom states breakfast is the most important meal of the day, skipping breakfast may actually help you control your appetite throughout the day. Skipping breakfast is also an easy way to implement intermittent fasting, which has a number of well-documented health benefits, including weight loss and improved weight management as you become increasingly fat-adapted.
Keep in mind that it takes about six to eight hours for your body to metabolize your glycogen stores and it's only after that that you actually start to shift to primarily burning fat as fuel. If you keep replenishing your glycogen by eating every eight hours, you make it far more difficult for your body to actually shift to fat burning mode, so when using intermittent fasting, make sure your fasting period is long enough (12-18 hours). You will need to start gradually though and take a few weeks or more to get to 12 hours and eventually longer.
I have revised my personal eating schedule to eliminate breakfast and restrict the time I eat to a period of about six to seven hours, typically from noon to 6 or 7 pm. Our ancestors rarely had access to food 24/7 like we do today, and it makes sense that our genes are optimized for intermittent fasting. On the days that I exercise in the morning, I will have two scoops of Pure Power Protein about 30 minutes after the workout to provide nutrients, especially leucine, for muscle growth and repair.
A growing body of intriguing research indicates that intermittent fasting may be a key weight loss tool – especially when combined with exercise in a fasted state – and this has been true in my personal experience as well. Since adopting this approach for the past few months I have lost two inches from my waist size and gained three pounds, which means I have lost body fat and gained muscle mass.
Health Benefits of Exercising on an Empty Stomach
Research has shown that exercising on an empty stomach is useful for preventing both weight gain and insulin resistance, which is a hallmark of countless chronic diseases. One of the explanations for this is that your body's fat burning processes are controlled by your sympathetic nervous system (SNS), and your SNS is activated by exercise and lack of food. The combination of fasting and exercising maximizes the impact of cellular factors and catalysts (cyclic AMP and AMP Kinases), which force the breakdown of fat and glycogen for energy.
This is why training on an empty stomach will effectively force your body to burn fat.
Intermittent fasting calls for you to exercise in late morning or early afternoon, and fasting (or eating only light raw foods, vegetable juice and/or whey protein or eggs) until 30 minutes after your workout. If you have trouble exercising on an empty stomach, you can include 20 grams of a fast-assimilating protein like a high-quality whey protein concentrate 30 minutes before your workout.
Exercise and fasting result in acute oxidative stress, which keeps your muscles' mitochondria, neuro-motors and fibers intact. You may have heard of oxidative stress before in a negative light, and when it is chronic it can lead to disease. But acute oxidative stress, such as that which occurs due to short intense exercise or periodic fasting, actually benefits your muscle. In fact, according to fitness expert Ori Hofmekler:
"[Acute oxidative stress] is essential for keeping your muscle machinery tuned. Technically, acute oxidative stress makes your muscle increasingly resilient to oxidative stress; it stimulates glutathione and SOD production in your mitochondria along with increased muscular capacity to utilize energy, generate force and resist fatigue.
Hence, exercise and fasting help counteract all the main determinants of muscle aging. But there is something else about exercise and fasting. When combined, they trigger a mechanism that recycles and rejuvenates your brain and muscle tissues."
The mechanism he refers to is triggering genes and growth factors, including brain-derived neurotropic factor (BDNF) and muscle regulatory factors (MRFs), which signal brain stem cells and muscle satellite cells to convert into new neurons and new muscle cells, respectively. This means that exercise while fasting may actually help to keep your brain, neuro-motors and muscle fibers biologically young. The combined effect of both intermittent fasting and short intense exercise may go way beyond helping you to burn more fat and lose weight; it may help you to:
Turn back the biological clock in your muscle and brain Boost growth hormone Improve body composition Boost cognitive function Boost testosterone Prevent depression
Exercise May Also Influence Satiety and Weight by its Effect on Gut Hormones
While we're on the topic of food and exercise, an interesting study presented at the 2011 meeting of the Society for the Study of Ingestive Behavior (SSIB) revealed that exercise may help control your body weight by altering the hormones released by your gut after a meal.4 In rats that exercised, increased levels of an inhibitory feeding hormone, amylin, were released when a meal was eaten, and a more rapid rebound of ghrelin occurred after the meal. Further, exercised rats treated with a gut hormone called CCK, which limits meal size, decreased their food intake more so than sedentary rats.
According to one of the study's authors:5
"Our new results indicate that the beneficial effects of exercise to control body weight might occur by altering the way in which meals release gut hormones that regulate food intake, and also by changing the sensitivity of individuals to these gut hormone signals."
Exercise is already known to increase sensitivity to leptin, the "satiety hormone" involved in appetite regulation, providing even more reason to make physical activity a regular part of your life, especially if you're struggling with overeating.
Tips for Fasting and Exercising Safely
While exercise and fasting help counteract muscle aging and boost fat-burning (compared to working out after eating), fasting incorrectly can cause more harm than good. To start, you need to make sure that you're not fasting to an unhealthy extreme. In other words, fasting does not mean that you starve yourself for days. Instead, intermittent fasting involves restricting your food intake during the day to a smaller time window (typically six to eight hours).
When you add exercise to the mix, you complete your workout while fasting, but this must be followed by a recovery meal within 30 minutes of your workout. This is very important and should not be skipped. Whey protein is ideal, as it is fast-assimilating and will provide you with the nutrients your muscles need for recovery. (Make sure to avoid any and all sources of fructose as this will sabotage the health benefits of your exercise! This means avoiding virtually all sports drinks and juices.) Then, you eat one single, main meal at night.
Skipping the recovery meal after exercise is very ill advised, as it can lead to brain and muscle damage. So please, do not take your fasting to the extreme by skipping this meal.
"When you implement intermittent fasting you put your body into a strong catabolic state. Your body is literally eating up and destroying damaged and injured brain and muscle cells. You rapidly accelerate this process when you exercise in this state. It's this very powerful synergy that will allow you to effectively rejuvenate your muscle and brain. This is the radical new approach that very few know about and even fewer have implemented.
The MAJOR danger though is that you will need to rescue your muscle tissue out of this catabolic state and supply it with the proper nutrients to stimulate repair and rejuvenation. If you fail to supply these nutrients at the proper time you will hurt yourself.
Your post exercise recovery meal is critically important. It's needed to stop the catabolic process in your muscle and shift the recycling process towards repair and growth. If you fail to feed your muscle at the right time after exercise, you won't just miss this window of opportunity to restore and build your muscle, you'll actually let the catabolic process go too far and potentially waste and damage your muscle."