True or False? Exercising on an empty stomach will help you burn more fat

Generally False… for a few reasons:

Weight and body fat loss or gain is determined by caloric balance. If, over the course of the day, you eat more calories than you spend, you’ll gain weight and body fat. If you spend more calories than you eat, you’ll lose weight and body fat. Your weight is not determined simply by what you burn during exercise.

It’s commonly believed that if you exercise on an empty stomach, you’ll burn more fat since your carbohydrate stores are almost empty. As such, your body will use up your fat stores to fuel your workout.

Before we discuss that, here’s an overview:

Fuel for exercise

When we eat carbohydrates (grains, breads, pastas, rice, cereal, fruits, sweets) it gets stored in our liver- to control blood sugar- and in our muscles- to fuel our exercise. The stored form of carbs is called glycogen. If you run out of glycogen when you exercise, you will “hit the wall” and have to stop.

Glycogen is one of the only fuels we can burn during anaerobic exercise- exercise that doesn’t require oxygen, i.e. short bouts of high intensity activities like sprinting, hockey, weight lifting. When there’s oxygen present, i.e. when you do aerobic activities like walking, running, biking, fat can be used as a source of fuel. However, to burn fat, you need to have some glycogen.

It takes 24-48 hours for your muscle glycogen stores to fully replenish- even if you’re eating a high carb diet. An endurance athlete will use up all of their muscle glycogen stores in 1-3 hours of continuous moderate-high intensity workout (depending on fitness level) if they don’t take in any carbs during exercise.
A weight lifter will deplete as much as 26% of their overall muscle glycogen during high-intensity strength training- however, research has shown that muscle glycogen depletion is localized in the muscles that are worked. As a result, if you train your legs, you may have lost 26% of your overall muscle glycogen but the glycogen in your leg muscles can be totally depleted.

So, if you didn’t deplete your glycogen stores in the last 2 days and have been eating a high carb diet and drinking enough fluids, when you wake up in the morning, regardless of whether you eat or not, your muscle glycogen stores will be full. However, your liver glycogen stores will be pretty much empty meaning your blood sugar may be low. The reason we tell people to have a pre-exercise snack or meal is to replenish liver glycogen stores which will maintain blood glucose levels, helping you feel more alert and energetic. However, this snack is not really used as fuel. When you workout, you’re burning what you’ve eaten and stored over the last 24-48 hours.

A single carbohydrate-rich meal will quickly restore your liver glycogen stores: an energy bar, a glass of OJ and a toast, a bagel, a sports drink, a meal supplement like ‘Boost’, a small bowl of cereal.

Burning fat

As for burning more fat when you exercise on an empty stomach- some small studies have shown that this is possible… but there’s a tradeoff: you can run low on energy. A 2000 study published in the International Journal of Sport Nutrition and Exercise Metabolism found that performance of moderate-to-high-intensity exercise lasting 35-40 min was significantly improved in those that consumed a moderately-high carbohydrate, low fat, low protein meal 3-hr before exercise compared to a similar meal consumed 6 hr prior to exercise. Various other studies have demonstrated the same thing. Exercisers are not able to exercise as hard or as long when exercising on an empty stomach.

If you’re not able to work out as long or as hard, you’re going to burn less total calories. So, regardless of the fact that you may be burning a little more fat calories, the total calories burned will be less and you will not lose more body fat. Moreover, because your blood sugar will fall as a result of your liver glycogen depletion, chances are you’ll be famished after your workout. Hunger is a side effect of low blood sugar. Experts point out that you’re more likely to overeat post-workout and therefore consume more calories, leading to weight and body fat gain!

Bottom line

The research has consistently shown that, for both endurance and power athletes, performance will suffer if you don’t consume enough carbohydrates during the day (you should be aiming for more than 50% of your total calories coming from carbs) since muscle glycogen is the limiting factor for any type of activity.
As for pre-exercise, it’s recommended you have a small snack or meal to top off your liver glycogen stores and ensure peak performance or peak calorie-burning.

Sources:

Girard Eberle, Suzanne. Endurance Sports Nutrition. IL: Human Kinetics. 2000.
Kleiner, SM; Greenwood-Robinson, M. Power Eating: Build Muscle, Boost Energy, Cut Fat, 2nd ed. IL: Human Kinetics. 2001.
http://www.jeffgalloway.com/nutrition/nancy/excercise_weight.html
Maffucci, DM; McMurray, RG. Towards optimizing the timing of the pre-exercise meal. Int J Sport Nutr Exerc Metab. 2000 Jun; 10(2): 103-13.
Smith, Heidi. Nutrition for the Long Run. Copyright “October 2003” by Heidi Smith.

Does High Fructose Corn Syrup make us fat?

Have you seen the new commercials put out by the Corn Refiners Association? They’re meant to convince us that the much talked about High Fructose Corn Syrup (HFCS) is no worse for us than table sugar or honey. For a while now, HFCS has been targeted as the cause of the obesity epidemic. That’s because the rise of obesity parallels the increased use of HFCS by food manufacturers, both of which started in the 1980s. By 1984, Coca-Cola had completely replaced sugar with HFCS. Corn sweeteners are made from corn, and corn is a subsidized crop and is therefore cheaper than sugar to use, explaining the huge increase in its use. In 2005, about 77 lbs of corn sweeteners were produced per capita in the US, compared to 35lbs in 1980.

Does HFCS make us fat?

According to most experts, including the Centre for Science in the Public Interest, and probably to the delight of the Corn Refiners Association, HFCS itself is not responsible for making people fat. Although far from natural, as the Corn people would like you to think, HFCS does start out as simple cornstarch- basically made up of chains of glucose molecules. Enzymes from cultured molds are then added to the cornstarch to break down the long glucose chains. To increase the sweetness, enzymes from various species of a bacteria are added to convert some of that glucose to fructose. HFCS is usually either 45% or 55% fructose. Table sugar, or sucrose, also contains glucose and fructose, in equal proportions. As such, it can be deducted that the physiological impact of both these sweeteners are similar.

However, a recent study published in the July issue of the Journal of Nutrition found that study participants given a drink containing more fructose than glucose (50% each and 75% fructose/25% glucose) converted sugar into body fat at a significantly higher rate than those given a drink of just glucose. These findings are interesting but it would be misleading to use these results to imply that fructose is responsible for increasing body fat. First of all, the study only had 6 young and healthy subjects. More importantly, however, we’ve known that we metabolize fructose somewhat differently than glucose but, even the lead researcher of this most recent study has said, we also know that fructose is not responsible for weight gain and dieters should not eliminate fruit, which have a high fructose concentration, from their diet. Excess caloric consumption results in weight gain. Incidentally, Americans are consuming an additional 200 calories per day compared to what they were eating 30 years ago.

Want to lose weight? Reduce caloric intake and that involves reducing all sugar intake- including HFCS.

Sources:

“Limiting Fructose May Boost Weight Loss, Researcher Reports”. http://www.sciencedaily.com/releases/2008/07/080724064824.htm

“Food Additives”. http://www.cspinet.org/reports/chemcuisine.htm

“Corn Refiners Ad Campaign Called Deceptive”. http://www.cspinet.org/new/200806231.html

Pollan M. The Omnivore’s Dilemma: A Natural History of Four Meals. Penguin Books 2006.

Willett W. Eat, Drink, and Be Healthy. Free Press 2001.

Nestle M. What to Eat. North Point Press 2006.

Schwarcz J. That's the Way the Cookie Crumbles. ECW Press 2002.

Post-exercise GI distress and dehydration

Over Thanksgiving weekend, my best friend ran a half marathon as training for his second marathon that he’ll be running in December. Even if it was just a training run and he had had a cold the week prior to the race, preventing him to run, James still finished in 4^th place with a time of 1:30:03! Not too shabby!

However, about an hour after the race, James started to experience incapacitating waves of stomach cramps that lasted over 24 hours. What caused this gastrointestinal distress?

The most likely explanation: dehydration.

Suzanne Girard Eberle RD explains in her book, Endurance Sports Nutrition, that during prolonged exercise, your body diverts blood from your colon to your active muscles and skin that need it more. When you’re dehydrated, this situation is exacerbated since dehydration causes a decrease in blood volume, so there’s even less blood available to the large intestine. This causes a whole array of gastrointestinal problems. It slows gastric emptying, meaning that food and fluids sit in your stomach rather than passing through your intestine, causing abdominal discomfort, bloating and cramping. The lack of blood flow can also seriously damage the walls of your colon, potentially causing ‘athletic colitis’, aka ischaemic colitis. Symptoms include diarrhea during exercise, but not at other times, extreme abdominal pain and bloody stools. If you experience these symptoms, you should go to the emergency room as it is a serious condition. There are 3 documented cases of elite triathletes that have had to have parts of their colons surgically removed as a result of athletic colitis. Luckily, early recognition and appropriate management, that includes intravenous rehydration and antibiotics, lead to complete resolution of symptoms and no long term damage.

Another indication that James was probably dehydrated is his performance. Although 1h30 is a great time for a half marathon, believe it or not, James is capable of running even faster! Studies have shown that for every 1% loss of body weight, athletes slow down by 2%. A 150-lbs runner that loses just 3lbs water (2% body weight loss), will slow down by 4%. At 8min/mile, that’s 20 seconds/mile. That’s a lot. Moreover, a loss of 2lbs water can increase your heart rate by 8 beats/minute- that’ll tire you out quickly.

Apart from dehydration, other possible factors that could have contributed to James’ stomach cramps include:

The intestinal jostling caused by running,

Exercise-induced changes in GI hormones,

Mental stress (he did want to impress me...!) that can actually slow down gastric emptying,

NSAIDs (Non-steroidal anti-inflammatory drugs). James took an Advil before the race. Many athletes take anti-inflammatory drugs (ie.s NSAIDs like Advil, Nuprin, Aleve, Actron) before or during long races to minimize pain. However, NSAIDS can cause stomach irritation. Moreover, taking NSAIDs when it’s very hot or when you’re dehydrated can potentially be dangerous as it has been shown to possibly contribute to hyponatremia (low sodium concentration in the blood) and kidney problems. When taking these drugs, be very aware of your fluid intake to prevent dehydration.

Other possible factors that can cause GI distress during exercise (but that were not factors for James) include:

Training status- the more trained you are, the less likely you are to experience GI problems.

Age- younger athletes are more at risk for GI problems- most likely because they may be less trained and have less nutrition knowledge and experience.

Intensity- The more intense the exercise, the more blood is shifted from the intestine to the active muscles, resulting in delayed gastric emptying and GI distress.

Caffeine- Can cause diarrhea and upset stomach.

Gels and too-concentrated liquid solutions- When highly concentrated solutions like gels, juice or soda pop are not diluted with water, they may cause stomach distress. Sports drinks, like Gatorade or Powerade, are diluted to the perfect concentration.

How James can avoid this next time:

Start out hydrated: Adults need about 8-10 cups non-alcoholic fluids a day in addition to drinking before and after exercise.

Stay hydrated: During exercise, drink early and drink often. Aim for 2-3 cups fluid (16-24oz)/hour. (A helpful tip: for the average adult, 1 gulp=1oz; for younger athlete, 2 gulps=1oz). Follow a pre-determined drinking schedule rather than relying on your thirst. Once you feel thirsty, you’ve likely lost 3% of your weight as fluid, resulting in a 10% loss of performance. Plain water is acceptable for activities under an hour (although a sports drink could give you the extra boost you need) but rely on a sports drink when exercising >1 hour.

Replenish your fluids: Weigh yourself before and after exercise- that weight lost is water, not fat! Drink 3 cups non-alcoholic fluids for every pound lost to replenish your fluids.

Congratulations James!

How to become as fat as a Sumo wrestler

Sumo wrestling is a way of life and requires a lifetime dedication. It can take up to 10 years to become a professional. Teenage boys join schools to learn the basics of Sumo and Sumo wrestling scouts choose the athletic ones with stocky builds. They won't choose the obese boys because that indicates a lack of discipline.

Sumo wrestlers are called rikishi.

A respectable rikishi weighs at least 200kg (440lbs) and up to 280 kg (616 lbs). There is no weight division so basically, the bigger you are, the better.

Steps to becoming as fat as a Sumo wrestler

Skip breakfast. Rikishis wake up at 4-5 am and will only have their first meal at midday. Not only does this slow down their metabolism encouraging fat storage, but they’re starving at this point and can eat 5-10 times the amount an average person will eat. Rikishis eat only 2 very large meals a day.

Eat very large amounts of food. One of the heaviest rikishis in history, at 285kg, could eat 10 bowls of stew*, 8 bowls of rice, 130 pieces sushi and 25 portions of barbecued beef at one sitting. Rikishis eats, on average, 10 000 calories a day.

*The traditional meal is a stew called chanko-nabe and is pictured above. It contains meat (fish, seafood, chicken, pork or beef) and is served with rice and vegetables.

Drink a lot of alcohol. Sumo wrestlers drink a lot of beer which contains a lot of calories and leads to weight gain.

Sleep after you eat. Sumo wrestlers sleep for 3-4 hours following their large meal. Perfect way to avoid burning off those calories.

If you do decide to follow these steps, be aware that this lifestyle is not without its risks. The average life expectancy of a rikishi is 65 years old, 10 years below that of the average Japanese male. Their risk of type 2 diabetes, high cholesterol, blood pressure, heart attacks and gout is much higher than the average population's. Their heavy weight is a strain on the joints, increasing their risk of arthritis. Due to their high alcohol intake, they are more prone to liver problems.

Sources:

http://www.discoverychannelasia.com/sumo/become_a_sumo_wrestler/index.shtml
http://abcnews.go.com/GMA/story?id=4209021
http://www.ajcn.org/cgi/content/abstract/29/10/1167

Spring cleaning: detox / cleansing diets

Gwyneth Paltrow does it. So does Angelina Jolie, Oprah, Liv Tyler, Ben Affleck and Christy Turlington (to name a few). Beyonce did it to lose 20lbs quickly for DreamGirls. I’m talking about “detox” or “cleansing” diets.

What are detox/cleansing diets?

There are different variations of detox diets but all claim to clean out our bodies of chemicals and dietary toxins. The supposed result: weight loss, increased energy, better digestion. Another claim is that by allowing the cells in the gut to rest, they are able to grow stronger, resulting in a healthier gut.

You can ‘detox’ by eliminating certain foods from your diet- Oprah recently followed a 21-d detox diet in which she eliminated animal products, sugar, alcohol, caffeine and gluten. The stricter versions are liquid diets- lemonade (followed by Beyonce and others) or juice fasts where followers will drink anywhere from 32 to 90 oz juice/24 hours, and even water fasts. Many of these diets also suggest enemas. These diets vary in time- from 1 day to a few weeks.

Do they work?

There is no scientific evidence available to support any of the claims these diets make- only people’s testimonials. Most health professionals, myself included, will tell you that our body is able to “detoxify” itself naturally. Abstaining from food will not help you be healthier. In fact, fibre’s role is to help clean out the gut- so a diet that’s rich in vegetables, fruits, whole grains, beans and lentils and other lean proteins and water would be the perfect detox diet!

With summer coming up, you may be tempted by this supposed “quick fix” to weight loss. However, for the most part, these diets and fasts are an ineffective weight loss solution. If you do lose weight, it’ll mostly be water weight and you’ll most likely regain it... quickly. Any diet that eliminates major food groups (or food, for that matter!) is not sustainable- definitely not a long-term solution. Moreover, many of these diets are extremely low in calories. As a result, your body goes into ‘starvation mode’- your metabolic rate will decrease so you’re burning less calories at rest. Moreover, your body will hold on to its fat stores (because it’s more energy-efficient) and burn lean muscle... something you obviously want to avoid. When you start eating again, your body will more easily store those calories as fat and, as a result, you’ll regain the weight faster.

You need to eat to lose weight!

These diets also lack major nutrients: protein, an essential nutrient in helping you maintain lean muscle mass during weight loss, as well as fat, an essential nutrient that, among other things, is essential in helping you feel full after a meal. As a result, people claim to always feel hungry on these diets... something that is not only uncomfortable but can cause irritability and lead you to eat irrationally afterwards. Beyonce was quoted as saying: “I was hungry, therefore I was evil. When we wrapped the movies, I was so excited... I ate a whole dozen Krispy Kreme doughnuts”. It was also reported that she quickly regained the weight she had lost on the diet... a fact that’s ignored by followers of the same diets!

A dietitian calculated that the Master Cleanse diet (a well-known detox diet that consists of drinking 96 oz of lemonade with maple syrup and cayenne pepper a day) is 1300 calories. A woman should never eat less than 1200 calories and a man, never less than 1500 calories. So, for a woman, 1300 calories isn’t drastically restrictive. However, it lacks major nutrients. Why not eat 1300 calories of fibre-rich vegetables, fruits, whole grains, lean proteins and drink water?! You’re more likely to stick to a meal plan that includes real healthy foods, you’ll lose weight, and you’ll also have more energy to exercise- an important key to long-term weight loss!

Oftentimes, these diets are used to “jump start” weight loss, ie. They start with a strict “detox” diet for a few days and follow it with a weight loss program. Maybe. A diet (under the supervision or guidance of a Registered Dietitian or doctor) that restricts certain foods, ie. alcohol, sugar, animal products (if replaced by vegetable protein), can be useful in motivating someone to kick-start a weight loss program and perhaps feel ‘cleansed’. As long as the diet is not overly calorically-restrictive and includes all the major nutrients, it can be an effective motivational tool to start a healthy weight loss program... although, not necessary.

What are the risks?

Evidently, the extreme diets, (fasting- no food) are extremely dangerous. However, even restrictive diets can be dangerous if you’re not replacing the nutrients you’re eliminating. As a result, speak to your doctor and/or a Registered Dietitian before embarking on any diet.

Many of these detox diets will rightfully warn pregnant and breastfeeding women and women trying to become pregnant against trying them. Children should not be put on these diets. These diets can widely affect blood sugar levels so people with diabetes and low blood sugar (hypoglycaemia) should avoid them as well.

If you’re recovering from an illness or injury, suffer from anemia, have weakened immunity (ie. elderly), have heart problems, psychological problems (depression, bipolar disorder, prone to eating disorders), are underweight and/or suffer from migraines, you should not embark on these diets- they can exacerbate existing illnesses or delay healing/recovery.

Apart from irritability, side effects of liquid diets and fasts can include GI problems, ie. diarrhea and/or constipation, dizziness, difficulty concentrating, fatigue, depression, headaches, fainting, irregular heart beats, dehydration and even death.

Drinking yourself fat

Augh... disgusting, eh?
But yeah for the NY Health Department for being pioneers in health promotion!

New Yorkers will all start seeing these ads in the next year as well.

Remember that milk can fatten you up too though...

If you currently drink 2 cups 2% milk a day, did you know that if you switched to 1%, you would lose 4 lbs a year?

And that if you switched to skim milk, you would lose just under 8lbs a year?

Don't drink yourself fat...

The Glycemic Index and the Glycemic Load

What happens when we eat carbs?

Some foods make our blood sugars spike really quickly and others, not so much. The foods that have an effect on blood glucose contain carbohydrates. When you eat foods containing carbs they break down to their basic component, glucose or sugar, in the intestine and glucose gets into the bloodstream. As a result, your blood glucose goes up. In response, your pancreas secretes a hormone called insulin that helps sugar get out of the blood and into your body cells that need sugar. Glucose is actually the main fuel for your brain and muscles.

However, when lots of glucose comes in at the same time, your pancreas secretes a lot of insulin at once resulting in a quick drop of your blood glucose. When your blood glucose goes down that quickly, you feel hungry and, as a result, eat again, leading to potential weight gain. Another thing that happens when there’s too much glucose that comes in at once is that your muscle cells start to resist storing the extra glucose. This extra sugar gets stored as fat and also contributes to weight gain.

There are carbohydrates that break down really quickly into glucose- so eating too much of those types of carbohydrates quickly causes your blood glucose to spike quickly, causing all this havoc.

David Jenkins and colleagues from the University of Toronto created a system that ranks carbohydrate foods based on how quickly they break down to sugar. This is known as the Glycemic Index. They compared the impact of different foods on blood glucose to the impact of standard foods like pure sugar on blood glucose. Pure sugar was given a Glycemic Index (GI) of 100.

Foods that have a GI of less than 55 are considered to have a low GI or low impact on blood glucose, 55-69 is a moderate GI and a GI of greater than 70 is considered high.

For example, black beans have a GI of 30. This means that they boost blood sugar 30% as much as pure glucose.

Although GI offers some useful information, it’s not the whole picture. For example, carrots have a GI of over 70. Carrots do have sugar that’s highly absorbable but the total amount of sugar is very small and therefore has very little effect on blood glucose. Luckily, there’s something called the Glycemic Load.

The Glycemic Load (GL) was developed by Walter Willett and colleagues at the Harvard School of Public Health and considers the total amount of carbs in a food as well as the GI. A GL of less than 10 is low, 11-19 is medium and more than 20 is high.

The Glycemic Load of carrots is 5.

Although most health experts, including Marion Nestle and Walter Willett, call GL and GI useful tools, they caution to not build your diet around it. Marion Nestle says she ignores the long lists of foods and their GI and GL values (I included one of those lists below) because not only do the numbers vary depending on the source, but they also vary depending on preparation and cooking methods. It all gets very confusing.

Not only that but if you add butter and cheese on top of a potato, the Glycemic Index will be lower (fat and proteins have no GI because they have no carbs) but calories and saturated fats increase. So just because a food or a meal has a low GI or a low GL, doesn’t mean it’s necessarily a good choice!

What you should focus on is how much food you’re eating and choosing less processed starchy foods (that usually have high GI and GLs anyway).

Health Benefits of choosing low Glycemic Index and Glycemic Load foods

In both the large Nurse’s Health Study and Health Professionals Follow-up Study, it was found that people who ate low fibre cereals and high Glycemic Load foods more than doubled their risk of type 2 diabetes.

Other research has shown that the excess sugar and insulin that comes from eating high GI and GL foods contribute to other chronic conditions like heart disease, breast cancer, colon cancer and polycystic ovarian syndrome.

Now, I haven’t read any of these studies (yet) but just summarizing from Willett’s book. However, it seems to me that people who eat higher fibre and lower GI and GL foods (like whole grains, legumes, vegetables) are those that are most likely to have healthier lifestyles- eat healthier, exercise more, don’t smoke, not overweight etc. than those that are eating low fibre and high GI/GL foods. So is it just the higher intake of high GL/GI foods that are contributing to these health conditions or is it a less healthy lifestyle?

Mike- hope this answers some of your questions. There'll be more to follow.

Glycemic Index and Load of foods: http://www.ajcn.org/cgi/reprint/76/1/5

Sources:

Nestle, Marion. What to Eat. 2006

Willett, WC. Eat, Drink, and Be Healthy- The Harvard Medical School Guide to Healthy Eating. Free Press 2005.