Carbohydrates, Fats and Proteins; How much and Why?

Substantial controversy exists over what percentage of food should be derived from which marconutrients. Macronutrients are Carbohydrates, Proteins and Fats. These nutrients are the 3 energy supplying nutrients for the human body.  Conflicting opinions between dieticians, body sculpters, internet health guru's, and even medical practitioners has made the area of weight loss and nutrition an unsigned roadmap. Should the consumer be eating high Carbohydrate diet containing wholegrains as once recommmended or in fact were these carbohydrates what led the western world into its current obesity epidemic. The aim of this article is to provide some guidelines for dietary intake and to provide some background information as to why these guidelines are in place. No financial gain is achieved from offering a unique opinion nore will i attempt to undermine others viewpoints for the sake of furthering a product.

Carbohydrates, Fats and Proteins. Carbohydrates and fats are the energy supply source for the body. The nervous system and in particular our brain relies on carbohyrates to funtion, our muscles utilize both fats and carbohyrates. At differing exercise intensities the utilization of these two macronutrients will change, with high intensity exercise requiring solely carbohydrates and low intensity using both.

Protein refered to as Amino Acids are the building blocks of the human body. There are both essential and non essential amino acids. Essential Amino acids are the same as essential fatty acids in that the body cannot create these amino acids from other compounds. Non essential amino acids can be derived from other protein consumed or stored in the body. 

Each one of these marconutrients serves a unique function and the body. The human body requires certain amounts of each of these macronutrients to funtion optimally.

Carbohydrates are they bad or are they good?

Carbohydrates are not bad, they are essential as are fats and proteins. Carbohydrates travel around the blood in the form of Glucose. Glucose is a simple broken down form of carbohyrates that exists in the blood stream. The amount of Glucose or sugar in the blood is measure in m.mols/Litre. Normal fasting Blood Glucose values fall between 3.6 and 6 mmol/l (approx 3.25g -5.4grams of glucose). After eating this value should remain below 7.8 mmols/l (7grams of Glucose). As you can see these values remain closely monitored.

It is estimated our brains and central nervous system require 130grams of glucose per day to function. This is because our brain cannot use fats as fuel. Glucose or ketone bodies (ketones are produced when carbohydrates are heavily restricted) can provide the fuel the central nervous system requires.

During high intensity exercises, glucose or glycogen is the only fuel source that can be used. This is due to glucose rather then fatty acid being utilized in anaerobic metabolism. See Energy Pathways. Carbohyrates are the primary source of Glucose for the body. Are they essential? meaning can the body exist without them. I believe carbohyrates are essential to the functioning of the human body. Glucose can be created from protein and ketone bodies from fats. Both these processes protect the nervous system by assuring Glucose in the body is always present. Reducing carboydrates to low or minimal values causes the bodies glycogen stores to drop. The result is protein must be eaten in larger does to supply the body with adequate glucose. Glycerol from fatty acid breakdown can also form ketone bodies. These ketone bodies serve as a replacement to carbohyrates for the brain. 

Although these process can occur recommendations are that their negative health benefits associated with producing glucose in this manner over a large period of time.

Carbohydrate storage

Carbohydrates that are consumed are broken down into Glucose, this glucose as mentioned travels in the blood, with the entire circulatory system containing around 5grams. Most meals will contain between 40-80 grams of carbohyrates. The result is the excess most be stored. If food has not been consumed for several hours the liver will take up much of the glucose and store it as glycogen. The liver holds around 100grams of Glucose. Muscle cells contain the largest source of stored glucose, it is estimated skeletal muscle contains 200-400grams of glycogen or stored glucose. 

Excess Glucose that cannot be used, or stored in the liver of muscle tissue is converted to body fat. Once converted to fat, the glucose cannot be changed back to Glucose and used by the brain.  

Are Carbohyrates making you fat?

As mentioned above excess carbohyrates can be converted to fats. Is this process leading to the rise in weight gain in western society? Long term research into the eating  behaviours of people in free living conditions suggests that overweight people compared to lean people tend to derive a higher percentage of there kilojoules from fat not carbohyrates (1,2). In many epidemilogical studies both fibre intake and carbohyrate intake are linked to lower body fat levels not higher.

The Graph above shows the habitual fat intake of lean compared to obese men and women (1). As you can see higher fat intakes are found in the overweight participants

Other studies have extended the link between fats and obesity and included fibre content (3,4) and Sugar intake (3). For an article on why fat, sugar and dietary fibre effect obesity see energy balance and correct eating principles

Controlled trials, which take a group of individuals and randomly assign them to a experimental and on none experiemental group have shown carbohyrates do not lead to weight gain. The below trials are ad libitum meaning the amount of food eaten is chosen by the individuals not the researchers. This enable the participants to choose when to eat based on there hunger levels. Calories are not purposely restricted, enabling these trials to closely mimic real life scenarios. These studies of low fat diets ad libitum diets show successful weight loss through  solely limiting fat intake and increasing carbohyrate intake (5,6,7). In each study the protein intake remained constant at 15-20% whilst the carbohydrate intake and fats intakes varied.

Similar to fats and protein, carbohydrates come in different forms. These difference impact how they are absorbed and used in the body.  Carbohydrates can be in the form of Complex Carbohydrates, which are joined Glucose molecules. These taste plain or savoury. Examples of complex carbohydrates are rice, pasta, cereals, breads and most vegetable. Simple Carbohydrate can be Glucose (this time in single form), Fructose, or Lactose. Fructose is a form of sugar found in fruits, it is also a large component of table sugar and most sugar additives. Lactose is the sugar found in milk

Most nutritionist recommend people eat a diet high in complex carbohydrates, with minimal added sugars. Sugars that are added to cereals, soft drinks, biscuits and lollies, come in the form of either sucrose or plain fructose or in form of corn syrup. These sugars are simple sugars which result in tooth decay and have been associated with weight gain. Research into fructose and obesity has revealed possible links between high fructose eating and weight gain. See article Fructose, Sugar and Weight Gain.

Complex Carbohydrates are instead those found in Breads, other grain based products, vegetables, legumes and beans. They are savoury in taste. These carbohydrates should make up the majority of the recommended 45-65% carbohydrate intake.

Fat is a source of energy to for the body during moderate to low intensity exercise. In times of extreme famine it can be used by the brain for energy via Ketone bodies but generally it is a fuel source for aerobic metabolism. This is lower intensity cardiovascular exercise such as that which is found in day to day activities, walking and light jogging. Fat should make up approximately 20-35% of the bodies total energy intake. See table below for values in grams.

Dietary Fat is involved in the storage of essential vitamins. Vitamins A, D, E and K are fat soluble. This means they are absorbed more readily in fats and fats will aid in there intake into the body. 

Fats are precursors to cholesterol metabolism and involved in hormone production. Extreme low fat diets or weight loss can result in what's known as Amenoria. This is where a women's menstrual cycle stops due to the diet, training or weight loss.

Low fat diets can also reduce a mans testosterone levels.

Saturated, Monounsatered or Polyunsaturated Fats.

Saturated Fats are found in visible animal fat, butter, milk and cheese. It is recommended that Saturated fat makes up no more then 10% of your total kilojoule intake. The American Heart Association recommends 7% your daily intake of energy. Some debate exists over whether saturated fats increase cholesterols and speed up arteriosclerosis, nutritional bodies support the notion that saturated fat do increase LDL cholestorols and which have a negative influence on health. See table below for recommended intakes in grams of saturated fats. Saturated fats generally contain higher amounts of cholesterol and as a result are recommended in smaller quantifies

Monounsaturated are those found in nuts, avocados, oats, olive oil and other plant based oils. Monounsaturated fats are linked with improved cholesterol profiles and improved blood pressure. For this reason its recommended including moderate amounts of monounsaturated fats in the diet.

Polyunsaturated fats are found in some oils such as sunflower and canola oil, fish oil and nuts. Omega 3 and 6 and 9 are all polyunsaturated fats. These fats are essential and not created in the body.  Research has supported that a higher consumption of Omega 3 results in a decreased incidence of heart disease, there is current studies into Omega 3's and arthritis, bipolar and depression. Research suggests no benefits are seen with Omega 3 and arthritis or Type 2 Diabetes. It's recommended omega 3's make up a small portion of your total fat intake. This can be achieved by including 2 serves of fatty fish per week. Cooking with canola oil or using margarines containing omega 3's will also boost intake. It is thought fish rather then plant based Omega 3's are needed for the benefits listed above

Proteins are involved in muscle repair and other essential functions within the body. Guidelines are for a moderate protein intake consisting of approximately 10-15% percent of the daily energy intake. Proteins eaten in excess can be converted to fats and stored as energy for later use. Alternatively during a sustained time without carbohydrates such as during endurance training or a low carbohydrate diets, proteins can be broken down and converted to glucose for use in the body.

This has advantages allowing for continued running or brain function in times of fasting. This can though result in a loss of muscle mass. For this reason a slightly higher protein intake is recommended in endurance athletes or those on energy restricted diets.

Proteins are present in all meats, milks, eggs and nuts. A 200g gram serving of meat contains approximately 50grams of protein. Consuming meat 5 times per week would ensure the average person achieves their protein requirements.

High Protein Diets and Weight Loss

Research shows mixed results on whether high protein diets result in weight loss. Some poorly controlled studies show large benefits. Well controlled studies where fat intakes remain equal and a portion of the daily intake of carbohydrates are replaced by protein tend to show no benefit to eating a higher protein diet. In studies where protein replaced fat or one of the diets is ad libitum (consumed at free will) and the other is not some results are found.  

Long term studies looking at obesity and dietary intake find no correlation between protein intake and weight loss. See (1,2,3) instead fats intake is correlated to weight gain, whilst carbohydrate and fibre intake is correlated to weight loss.

Research into the risk of high protein diets and renal function is unclear. Short term studies show no negative effects, although calcium excretion is high which could affect bone strength later in life. Chronic effects of high protein diets on the kidneys are unknown. This is part of the reason why moderate protein diets are recommended. Also foods high in protein tend to also contain larger amounts of saturated fats and cholesterols, both of which should be avoided in excess.

References: 

(1), Diet composition, energy intake, and exercise in relation to body fat in men and women.

W C Miller et al. Copyright © 1990 by The American Society for Clinical Nutrition

(2)Dietary fat and body fat: a multivariate study of 205 adult females.

L A Tucker and M J Kano. Copyright © 1992 by The American Society for Clinical Nutrition

(3) Dietary fat, sugar, and fiber predict body fat content ?™

Wayne C Miller et al. Journal of the American Dietetic Association

Volume 94, Issue 6, June 1994, Pages 612–615

(4) Predictors of weight gain in the Pound of Prevention study

Sherwood NE et al, International Journal of Obesity and Related Metabolic Disorders : Journal of the International Association for the Study of Obesity[2000, 24(4):395-403]

(5) Weight loss during 12 week's ad libitum carbohydrate-rich diet in overweight and normal-weight subjects at a Danish work site.

Siggaard R, Raben A, Astrup A. Obes Res. 1996 Jul;4(4):347-56

(6) Effects of an Ad Libitum Low-Fat, High-Carbohydrate Diet on Body Weight, Body Composition, and Fat Distribution in Older Men and Women: A Randomized Controlled Trial.

N. Hays, et al. Original Investigation January 26, 2004

(7) Long-term effects of ad libitum low-fat, high-carbohydrate diets on body weight and serum lipids in overweight subjects with metabolic syndrome

Sally D Poppitt, et al.

© 2002 American Society for Clinical Nutrition