THE TRUTH ABOUT FAT, CARBS AND WEIGHT GAIN

How many times have you heard “The fat in pizza will make you fat” or “the fat from deep fried foods will make you fat”? Countless, right? But truth couldn’t be farther than this. I myself believed, for the longest time, that a high-carb low fat diet is the holy grail of weight loss. But little did I know...

The recent interest in Atkins and South Beach diet and all the related success stories have compelled researchers to re-think the “fat will make you fat” mentality. To understand this, one has to understand the mechanism by which fat is stored in the body and the role of Insulin in weight gain. Fat in the diet converts to fatty acids and carbs in the diet convert to glucose in the blood stream. The role of pancreas in the body is to regulate blood glucose levels and when ever the glucose level in the blood rises, the pancreas produce insulin to counteract it. The insulin then takes away the blood glucose and converts it into glycogen that is stored in the liver and the muscle cells. Once the muscle cells and liver reach their full glycogen storage capacity any excess glycogen converts to fat. This is where added muscle mass from weight training comes in handy for storing the glycogen and prevent fat conversion. Fat doesn’t get stored as fat until it is acted upon by insulin and figure 1 shows how the blood glucose level rises with time after ingesting a carb or fat meal. It’s clear that fat doesn’t cause a rise in blood glucose level and neither does it elicit an insulin response from the pancreas as illustrated in figure 2.

Figure 1. Blood glucose levels after 100g of carbs or 40g of fat. [Ref 1]

Figure 2. Blood insulin levels after ingesting 100g of carbs or 40g of fat. [Ref 1]

The other aspect of this scenario is the delayed response of the glucose/insulin system. From figure 1 you can see that the blood glucose levels come back to normal levels within about 90 or so minutes while the insulin levels remain high, this causes your blood glucose to fall below normal levels, making you hungry again. As a result you consume more carbs. This sets off a vicious cycle, which if continued for long periods of time, makes the body insulin resistant and the more you eat the more insulin gets triggered causing more weight gain and more hunger pangs, making obesity inevitable. [Ref 2, 3]. The other affect of insulin is to suppress the production of Lipase, a hormone responsible for metabolizing fat in the cells into fatty acids.

The only way fat from diet gets stored as fat in the body is when insulin acts upon fatty acids and drives it into cells as stored fat. And from figure 1 and 2 its easy to see why fat by itself cannot contribute to weight gain. But if fat is consumed with carbs then it would contribute to fat gain. No wonder pizza, donuts and cheeseburgers are some of the most notorious weight gain foods because they combine fat with carbs.

So now that you have gained weight the next question is how to lose it? Well, the only way to lose fat is to metabolize it into fatty acids and use up as energy. This will happen in one and only one condition, that is, when you deprive the body of its present source of energy, glycogen. This can only happen by:

1) Starving.
2) Limiting the consumption of carbs and relying on fat and protein as the primary source of energy.

Obviously the first approach doesn’t work as it slows the metabolism and forces the body to go into starvation mode, thus making further fat loss impossible. The second approach is the gist of all the modern weight loss diets. The Atkins relies on protein and fat as the primary source of energy with very little carb. The South-Beach relies on high protein, ‘healthy’ fats and limited quantities of ‘healthy’ carbs for fuel. But what is a ‘healthy’ carb? This begs the question: are all carbs created equal? This is a topic for my next post…

References:

1. Robertson MD, Henderson RA, Vist GE, Rumsey RDE. Extended effects of evening meal carbohydrate-to-fat ratio on fasting and postprandial substrate metabolism. Am J Clin Nutr 2002; 75: 505-510.

2. Bruning JC, Gautam D, Burks DJ, et al. Role of brain insulin receptor in control of body weight and reproduction. Science 2000; 289: 2122-5.

3. Odeleye OE, de Courten M, Pettitt DJ, Ravussin E. Fasting hyperinsulinemia is a predictor of increased body weight gain and obesity in Pima Indian children. Diabetes 1997; 46: 1341-5.

AEROBICS OR WEIGHT TRAINING

What’s better for fat loss: Aerobics or Weight Training?

Energy expenditure in the body from any activity follows one of three pathways:

1) Aerobic: Any activity that is performed at a low to moderate intensity for more than 90 seconds, allowing oxygen to release energy through metabolism, is usually called an aerobic activity or more commonly referred to as cardio.

2) Anaerobic (ATP-CP): Any activity that utilizes Adenosine Tri-Phosphate (ATP) stored in the muscle cells. ATP is the immediate source of energy and is exhausted in about 3-5 seconds during a muscle contraction.

3) Anaerobic (Lactate/post ATP): As soon as the ATP in the cells is exhausted the body resorts to the breakdown of glucose for energy. This results in the production of lactate and hydrogen ions, ultimately leading to fatigue.

Cardio or aerobic exercise uses the Aerobic energy pathway while resistance or weight training uses the two anaerobic energy pathways. During exercise cardio burns about 20% more fat compared to weight training. But the flip side to this is that weight training results in increase of muscle mass that continues to burn calories in the rest state, thereby increasing your basal metabolic rate (BMR). Muscle cells are active tissues that require the conversion of blood glucose (from food) to glycogen thereby restricting the conversion of food calories to fat. So considering the long term fat burning capabilities of weight training vs. cardio, the former is the clear winner.

Both types of exercises have some pros and cons. The pros in favor of cardio are:

1) Increased cardiovascular function: the increase in the oxygen requirements when doing cardio increases your heart-rate since there is a higher need for oxygen carrying blood supply to the working muscle tissue.

2) Decrease in body fat: cardio exercises increase the capacity of working cells to absorb oxygen and glucose that are necessary for energy expenditure. This lowers blood glucose thereby reducing the calorie to fat conversion during the activity.

3) Cardio is fun and safe: Swimming, bicycling, jogging, brisk walking can all be fun.

The cons against cardio are:

1) Decreased muscle mass: The human body is an intelligent system and any endurance based exercise will, in order to maximize the efficiency, shed any unnecessary weight be it fat or muscle. So in effect cardio doesn’t discriminate between fat loss and muscle loss and only the muscles involved in the endurance exercise will be partially spared while the other muscles will atrophy. That’s why marathon runners have puny little chests and toothpick arms and not very big legs either.

2) Decreased strength/power/speed: again related to atrophy of all unrelated muscles.

3) Duration of activity: Aerobics has to be of a certain duration to be effective for fat loss. The energy for the first 20 or so minutes comes from either blood glucose (from food) or from muscle glycogen. Body fat is only used up after muscle glycogen stores are depleted. So in order to burn any fat the aerobics activity has to be done longer than 20-30minutes.

Likewise the pros in favor of weight training are:

1) Increased cardiovascular function: Even though anaerobic exercises don’t require the added oxygen to burn calories but nevertheless require the transport of nutrients like protein, amino acids and blood glucose to the working cells, thereby increasing the circulation and heart rate, although not as much as in a cardio workout.

2) Decrease in body fat: weight training increases muscle mass. The muscle cells constantly convert blood glucose to glycogen thereby reducing the calorie to fat conversion. This effect happens long after the activity has ceased. As a reference about 3lbs of muscle burns 120 calories/day even when it’s inactive. So if you gained 10lbs of muscle (which could perhaps take over a year of intense weight training) you would be burning the same amount of calories per day that a 140lb person would do in a jogging session at 5 mph for 45 minutes every day. Considering that you could be sleeping and still burn as many calories as the jogger, I think it’s a bargain worth shooting for.

3) Increased muscle mass: Isn’t that obvious.

4) Increased strength/power/speed: this one is also obvious. Consider the leg muscle, who do you think is stronger and more powerful and moves faster, a sprinter or a marathon runner? The sprinter of course!

5) Body Sculpting: With weight training you have the flexibility to sculpt your body to desired shape. If you want big arms there are exercises for just that. If you want big chest or shoulders, there are exercises for that. If you want a “V” taper to you upper body, there are back exercises for that. And if you want wash-board six-packs there are exercises for that.

6) Age-reversal effect of Weight Traning: Many researchers have shown that moderate amounts of weight training releases human growth hormone and testosterone, the two hormones that have shown age-reversal effect in humans. In several cases people that performed weight training demonstrated muscle mass, cardiovascular fitness, coordination and bone density comparable to those who were 20 years younger than them.

And the cons against weight training are:

1) Weight training can be dangerous: Its best to have a certified trainer teach the basic moves of weight training for safety reasons especially in compound body exercises like the squat, bench press and the dead lift. Don’t do it based on some videos you have watched on youtube.

2) Weight training is not as much fun as cardio: What is fun about repeatedly moving a certain weight from point A to point B set after set?

Physical fitness is a compromise of cardio-respiratory endurance, strength, flexibility, power, speed, coordination, agility, balance, accuracy and toughness. To pursue fitness excellence you must physically train to “optimize” your performance in all of the physical abilities and not “maximize” your performance in any one ability at the expense of all others.

I believe to get the best results one has to use a combination of both types of training methods. I have found that its best to do cardio and weight training on separate days or at least keep the workouts separate, for example do aerobics in the morning and weight training in the evening or vice versa. No matter which method you choose, remember that the best results come from perseverance and don’t happen overnight so stick to it and the results will follow.

Here is some additional reading on this subject:

http://www.womenshealthmag.com/fitness/cardio-vs-strength-training-workouts?page=1