Monday, September 24, 2012


The macronutrients: Carbohydrate, protein and fat

Which ones and how much??


There is currently a lot of debate regarding the ratio of carbohydrate versus protein that should make up our diet, especially when we are trying to lose weight (or gain muscle).  High protein diets are currently the “in thing” and everybody seems to be trying to avoid the “dreaded carbohydrate”.

Here are some facts I have gathered that help justify why the plate model  (pictured in my previous post) - ¼ of your plate low GI carbohydrates, ¼ low saturated fat protein (animal and/or plant sources) and ½ plate low-starch vegetables, is what I recommend to my clients.

The basics

Energy content of nutrients:

CHO (Carbohydrate)
Vitamins, trace elements
And minerals

So, one gram of fat contains about twice the amount of calories as one gram of carbohydrate or protein.

Also, note how high the energy density of alcohol is!

Macronutrients are broken down into energy in the following order:

1.    Alcohol
2.    Carbohydrate and Protein
2.    Fat

(note: in most circumstances when alcohol has not been consumed, protein is immediately taken up by muscles for repair and rebuilding , thus carbohydrate is the first energy source to be used.)

Evidence supporting increasing protein in the diet

A review of studies undertaken by Halton & Hu (2004) in the Journal of the American College of Nutrition found that convincing evidence is present to suggest that protein exerts an increased thermic effect when compared to fat and carbohydrate.  The thermic effect of a food is, in essence, the amount of energy required for that food to be digested and absorbed, plus the amount of energy required to dispose of its waste products.  The thermic effect of protein is approximately 20-35% of energy consumed, whereas the thermic effect of carbohydrate and fat is only in the range of about 5-15%. 

The same study examined the effect of protein on satiety and subsequent energy intake.  The available evidence suggested that protein rich foods increase satiety and thus decrease subsequent energy intake, at least in the short term, although it is difficult to separate these results from the effects of palatability, food mass, energy density, fibre and glycaemic index. (Halton & Hu, 2004)

Halton and Hu (2004) also noted that the studied data suggested that exchanging refined carbohydrates for protein improved blood lipid profiles, reduced blood pressure and reduced the risk of coronary artery disease.

Higher protein diets have also been associated increased lean muscle body composition when consumed in association with exercise.  Having an adequate protein intake when on a calorie deficient diet is essential to prevent muscle wasting.

Evidence against high protein diets:

Increasing protein intake leads to a greater production of nitrogen (waste product of protein digestion) and therefore urea, increasing the load on the kidneys (nitrogen is excreted from the body via the kidneys).  In patients with decreased kidney function, or at risk of decreased function, such as diabetics, this can be potentially dangerous.  High protein diets also have the potential to increase the risk of gout, due to higher levels of uric acid in the blood and to interfere with calcium metabolism, increasing the risk of osteoporosis.  (Nutrition Australia, 2006)

It is important to note that, as seen in the above table, the energy density of protein is much the same as that of carbohydrate.  If protein intake is in excess of that required for growth and repair by the body, it is simply broken down and used for energy; or, if calories ingested is greater than calories consumed, stored as fat.

Some people—such as body builders and weight lifters—adopt high protein diets based on the theory that muscle consists of protein, and that high protein intake will lead to greater muscularity. This argument is analogous to the belief that if a little vitamin A is good for you, a lot of vitamin A is even better. In fact, high doses of vitamin A are toxic (for example, excessive vitamin A intake has led to deaths in stranded Antarctic explorers who ate the livers of their husky dogs).

Similarly, protein intake above about 1.5-1.7 grams per kilogram of body weight is not only pointless, but potentially harmful. (Nutrition Australia)

Evidence for restricting carbohydrate intake:

The rationale behind carbohydrate restriction is that, in response to lower glucose availability, changes in insulin and glucagon concentrations will direct the body away from fat storage and toward fat oxidation. (Westman, et al., 2007)

Recent studies have shown that under conditions of carbohydrate restriction, the body shifts from burning glucose and fatty acids for energy to fatty acids (from dietary fat and adipose (fat) stores) and ketones (from dietary fat, protein and adipose stores).  Glucose dependent tissues (i.e. red blood cells, retina, lens and renal medulla) receive glucose through gluconeogenesis (glucose production at the liver) and glycogenolysis (release of glucose from muscle glycogen).  Even if no dietary carbohydrate is consumed, it is estimated that 200 g/day of glucose and be manufactured by the liver and kidney from dietary protein and fat. (Westman, et al., 2007)

Ad-libitum fed carbohydrate-restricted diets have been shown to reduce appetite, facilitate weight loss and improve markers of cardiovascular disease such as fasting triacylglycerols, HDL cholesterol and the ratio of total HDL cholesterol. Low carbohydrate diets have been shown to improve glycaemic control and insulin resistance in otherwise healthy people with Type II diabetes. (Westman, et al., 2007)

Whereas the loss of lean body mass is typical with weight loss, under certain circumstances when sufficient dietary protein is provided, a LCKD (low carbohydrate ketogenic diet) may preserve lean body mass even during hypoenergetic conditions of weight loss (Westman, et al., 2007).

The elimination or reduction of dietary carbohydrates removes many processed foods from the diet. (Westman, et al., 2007)

Evidence against carbohydrate restriction:

On a low carbohydrate diet, the body is forced to use some of its glycogen (the form of carbohydrate that is stored in the liver and muscles) to maintain a normal blood sugar level.  Some water that was stored with the glycogen is also released and excreted, adding to short-term “weight” loss, but note, this is not FAT loss! (Nutrition Australia, 2006)

Many low carbohydrate diets that restrict intake of plant foods such as certain fruits and vegetables are unlikely to supply sufficient quantities of dietary fibre and some vitamins and minerals.  (Nutrition Australia, 2006)  Plant foods also contain a myriad of other chemicals (phytochemicals) whose value to health is not yet fully understood, but restricting these foods could have more detriment to our health than we already know.  Evidence shows that increased consumption of a wide range of plant-based food sources is associated with improved health and increased life expectancy (Nutrition Australia, 2006)

Due to the elimination of food groups rich in essential vitamins and minerals, VLCKD require vitamin, mineral and fibre supplementation in order to prevent deficiency symptoms and constipation.  (Westman, et al., 2007).  Reported side effects include: constipation, headache, muscle cramps, diarrhea, weakness and skin rash. (Westman, et al., 2007)

Carbohydrate is the most direct and preferred source of glucose that not only powers our muscles, but also provides fuel for our brain.  This means that high-protein, low carbohydrate diets have the potential to interfere with the efficiency of both mental and physical work. (Nutrition Australia, 2006).

Studies on these diets have only been carried out, to date, in the short-term and longer study durations are required to determine adverse event profiles.

But what the evidence does not take into account:

Despite the evidence for and against particular macronutrient ratios, these studies all fail to take into account the psychosocial aspects of diet and nutrition; that is, how we feel about food, how it tastes and the other ways in which it is used in our lives, other than purely for an energy source.  I will not go into this in depth at this time, but we all know that there is more to eating healthy than simply knowing what to and not to eat and, as mentioned earlier, any diet that restricts ANY food group has the potential not only to be unbalanced, leading to deficiencies, but also to lead the dieter down the path of the binge-diet cycle, ultimately resulting in GREATER weight GAIN!

IN ADDITION: I do not believe that one should have to consume expensive vitamin or mineral supplements in order to fulfill their body’s requirements while putting themselves through a restrictive diet purely to be thin.  Any diet that does not provide all of the nutrients we require for our bodies to function efficiently IS NOT balanced and should not be used for long-term health (unless under specific guidance by a practitioner).

So, in summary, here is my recommendation of protein to carbohydrate ratios:

Include protein at every meal, in order to take advantage of the thermic effect of protein and its effect on satiety.  Choose lean (low saturated  fat) proteins from both plant and animal sources.  Choose protein instead of refined carbohydrates (hi GI carbohydrates, such as sugar), but do not increase protein intake to the detriment of low GI, nutrient rich fruit and vegetable intake.

Gram for gram, balance low-glycaemic index carbohydrates with lean protein sources in roughly equal amounts, but, as per the plate model, make up the majority (50%) of your plate with fresh, low starch salads and vegetables.

NEXT: Proteins, Carbohydrates and Fats, the good, the bad and the ugly.

Now that we know generally what our plate should look like and why, we will go through what are the BEST choices of foods to fit into these macronutrient categories.

Halton, T. L., & Hu, F. B. (2004). The Effects of High Protein Diets on Thermogenesis, Satiety and Weight Loss: A Critical Review. Journal of the Americal College of Nutrition , 23 (5), 373-385.
Nutrition Australia. (2006). Nutrition Australia: Nutrition Fact Sheet. High Protein Diets .
Westman, E. C., Feinman, R. D., Mavropoulos, J. C., Vernon, M. C., Volek, J. S., Wortman, J. A., et al. (2007). Low-Carbohydrate Nutrition and Metabolism. Americal Journal of Clinical Nutrition , 86, 276-84.

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