Everyone is Different.

Updated text in bold green.
If there is one thing that I have learned over the years of research into Diet and Nutrition, it's this: Everyone is Different. When I first discovered Low-carb Diets (thanks to the late Dr Atkins), I thought that it was the One True Diet, and I became a bit of an "Atkins Diet" bore telling everyone how wonderful it was and suggesting that everyone should be on it.

I now know that what suits me doesn't necessarily suit someone else. So why do "Healthy Eating" guidelines assume that everyone is the same and tell everyone to get 15% of their total calories from proteins, 55% from carbohydrates and 30% from fats?

To illustrate just how different people are, here's Fig. 2 from Determinants of the variability in respiratory exchange ratio at rest and during exercise in trained athletes. Used with permission.

Respiratory Exchange Ratio (RER) (a.k.a. Respiratory Quotient (RQ)) is the ratio of carbon dioxide breathed out to oxygen breathed in. This ratio depends on the fuel that the body is burning for energy. For example, if the body is burning 100% fat, RER = 0.7. If the body is burning 100% carbohydrate aerobically, RER=1.0. If the body is burning 100% carbohydrate anaerobically (flat-out sprinting), RER > 1.0. RER goes up and down depending on intensity of exercise, food intake (eating protein and/or carbohydrate increases it and extended fasting reduces it). Increasing cardiovascular fitness reduces RER.

The top diagram is a histogram of fasted RER and % fat oxidation vs. number of subjects. At the left-hand end of the histogram, there are two cyclists with a fat oxidation of 93 - 100%. At the right-hand end of the histogram, there is one cyclist with a fat oxidation of 20 - 27%.

There's a helluva big difference between burning 93 - 100% fat at rest and burning 20 - 27% fat at rest. Interestingly, average fat oxidation is 66%, which means that average carb oxidation is 34%. So, on average, at rest, people burn twice as much energy from fat as from carbs. So why do current "Healthy Eating" guidelines recommend almost twice as much energy from carbs as from fats for everyone, including sedentary people?

As exercise intensity increases, the peak in the histogram shifts to the right as shown in the lower diagram. At 25% full work-load, mean fat oxidation is ~53%. At 50% full work-load, mean fat oxidation is ~37% and at 75% full work-load, mean fat oxidation is ~13%.

I suspect that at 100% full work-load, mean fat oxidation is 0% i.e. 100% of energy is obtained from carbs when sprinting flat-out. Somebody on a very low carb diet like Atkins induction (~20g net carbs/day) could keel over with hypoglycaemia if they exercise for any length of time at this rate.

As there is so much variation from person to person, you must find out for yourself your own optimum proportions of proteins, fats and carbohydrates and these depend upon the intensity and volume of exercise you do. It all sounds a bit complicated but it isn't really.

Just apply the principle of "Eat, monitor and adjust accordingly" as Toxic Toffee (ex-Muscletalk member) always used to say. The eating bit I will advise on in future Blog posts. The monitoring bit does not involve the use of bathroom scales.

Hang on, isn't "dieting" all about losing excess weight? Not necessarily. Remember the old joke: Q. What's the best way to lose 5lbs of ugly flab? A. Cut your head off! As your body is made up of water, muscle, fat, bones, cartilage, tendons, organs, glycogen, skin etc and your scales can't tell the difference between them, losing weight the wrong way can make you less healthy. However, losing weight the right way will make you more healthy.

If you starve yourself or skip breakfast or go for a fast run before eating breakfast, as your body is lacking in glycogen and amino acids, a large amount of a corticosteroid hormone called cortisol is secreted which converts muscle into amino acids, then glucose. It also suppresses your immune system and weakens your skin and bones.

Unless you have a lot of muscle to spare, it's body-fat that you should be losing, and to monitor this, either use a tape-measure around your waist, or check how loose/tight your clothes are, or strip-off and jump up and down in front of a full-length mirror. As Big Les (Muscletalk Moderator) says, "If it jiggles, it's fat!".

So, what happens if you eat too many carbs but your body doesn't burn them fast enough? Initially, carbohydrate intake tops-up liver and muscle glycogen stores, which increases carb-burning to compensate. The liver can store about 70g of glycogen and muscles can store about 400g of glycogen. If, despite increased carb-burning, more carbohydrate is consumed than is burned, glycogen stores continue to fill. When glycogen stores become full, RER increases to 1.0 and 100% of energy is derived from carbohydrate. Getting 100% of energy from carbohydrate means that zero fat is burned, so filling glycogen stores by eating loads of carbohydrate is not a good idea if you want to burn body-fat. Once glycogen stores are full, any additional intake of carbohydrate beyond that which is burned passes through the lipogenesis pathway - this basically means that carbs are turned into fat - which you end up wearing as body-fat. But there's even worse news. On the way to being worn as body-fat, fat is in the blood as triglycerides. This is bad for the cholesterol particles in your blood. See the Blog on Cholesterol and Coronary Heart Disease. What happens if you eat too few carbs? As stated above, a "carb-burner" taking in insufficient carbs could get hypoglycaemia.

How many grams of carbohydrate per day does it take to promote lipogenesis? Someone at rest burns ~1kcal/minute. If this is derived 100% from carbohydrate, this is equivalent to 0.25g of carbohydrate /minute, or 15g of carbohydrate /hour, or 360g of carbohydrate /day. Therefore, sedentary people who consistently eat more than 360g of carbohydrate /day will produce significant triglycerides. People who have The Metabolic Syndrome/Syndrome-X (a high proportion of people who have excess belly fat) have increased lipogenesis and higher serum triglycerides than healthy people.

Just discussing weight again for a moment, it's often said that all diets are the same, as weight loss is all about calories. This is true. See Is a Calorie a Calorie? However, body composition is determined by a combination of macro-nutrient proportions (i.e. the relative amounts of protein, carbohydrates and fat that you eat) and the intensity and volume of exercise.

So, if all you're interested in is weight loss, just count calories. If however, you wish to lose body-fat without losing muscle, you need to know how to determine what proportions of proteins, carbs and fats to eat (it's not that critical, but many people get it totally wrong). You need to know the difference between good carbs and bad carbs and good fats and bad fats. You need to know the best times to eat proteins, carbs and fats (it's not that critical, but many people get it totally wrong). You need to know the difference between good exercise and bad exercise.

Cont'd on We are not all the same.