Supplement research

Protein Supplements

Introduction

Protein shakes offer a convenient form of protein for the busy individual. Protein has many important roles in the body including structure (e.g. muscle and bone), immune function, growth and repair.

Protein Requirements

Protein requirements have been estimated using a variety of techniques. Protein requirements are expressed as the amount of protein (g) required per kilogram (kg) of an individual's body weight, per day.

It has been estimated that the protein requirements for sedentary individuals within a healthy population are approximately 0.8g/kg/day.
There has been considerable debate whether physical exercise increases daily protein requirements.

Do physically active individuals need more protein?

Overall there seems to be evidence that exercise increases protein requirements. How much these requirements are elevated above that of sedentary individuals is still a matter for considerable debate. The table below shows the estimated protein requirements for individuals taking part in a different types of exercise, based on current knowledge and research on protein metabolism.

Table: Estimated Protein Requirements

Timing of Protein Intake

One important role for protein is for muscle recovery. During strenuous exercise some protein in the muscle is broken down. There is some research suggesting that taking protein and carbohydrate within half an hour of finishing exercise may help the process of building and repairing muscle (1-3). Taking protein with some source of carbohydrate has been shown to be beneficial because the carbohydrate will increase insulin levels which decrease muscle protein breakdown and may stimulate the uptake of protein into the muscle. The administration of protein appears to enhance muscle protein synthesis. There is also some evidence that consumption of protein before exercise may be beneficial. A recent study by Tipton et al showed a greater protein balance after exercise when a protein and carbohydrate beverage was consumed prior to resistance exercise (4). This area warrants further investigation. These studies would suggest that for those aiming to maximise muscle size, the consumption of a protein/carbohydrate rich snack prior to and after resistance training might be of benefit.

Types of Protein

There are many types of protein found in various plant and animal-based foods. Two common proteins used in protein supplements are Whey and Soy proteins

Whey Protein

Whey proteins are well known for their high nutritional value. Whey protein is one of the major proteins present in milk. It is absorbed at a faster rate compared to the other major milk protein, casein (5). Whey also contains a higher proportion of branched chain amino acids which results in a synergistic effect with insulin, while the secretion of the hormone glucagon is lower (6). This higher insulin: glucagon ratio may support greater protein synthesis after consumption of whey protein.

Some studies have suggested that the slower rate of casein may prove beneficial (4,7). Although casein stimulates protein synthesis to a lesser degree than whey, it appears to promote greater net protein deposition by producing a greater reduction in protein breakdown. This concept requires further investigation.

As well as having nutritional roles whey proteins are also responsible for many of the anti-infection, immunomodulatory and growth modulatory activities observed in milk. Bioactive proteins can be released from whey protein. Some of these bioactive proteins may have important physiological roles in the body, but more applied human clinical testing is required before the full impact of their physiological roles are fully understood. It is thought that some of these protein fractions such as immunoglobulins may stimulate our immune system.

Whey Protein Processing

There are several different processing techniques used to manufacture whey protein powders. How these proteins are processed during manufacturing can influence their availability to muscle.
Whey protein powders can contain whey protein isolates (using ion exchange or microfiltered methods) or whey protein concentrates (using ultrafiltration method).
The whey concentrates offers good value for money. They do contain more fat and carbohydrate than whey protein isolates. Whey concentrate provides about 80% protein per weight. The carbohydrate content is 3-8%% and the fat content 5-8%.
Whey protein isolates from microfiltration contain about 90.5% protein, with 0.8% carbohydrate and 0.3% fat.

Whey protein isolates from ion exchange contain 93.5% protein, 0.6% carbohydrate, and 0.3% fat. There is some concern that the ion exchange method may partially destroy some active component e.g. immunoglobulins.

Soy Protein

Another popular protein used in protein powders is soy protein. Soy protein is the only plant-based protein, which is considered a complete protein i.e., contains all essential amino acids. Soy is dairy free and so may benefit those who are unable to tolerate dairy products.

One study has shown that soy-based protein drinks may have the additional benefit from the isoflavanoids they contain (8). This study carried out on moderately active males showed some immune benefits. These included increased antioxidant status and a reduction in inflammatory stress following exercise. Further well-controlled studies are needed to confirm or refute this finding.

One animal study has shown that the intake of soy protein relative to casein (one of the major milk proteins), increased levels of the hormone cortisol which resulted in an upregulation of muscle protein breakdown (9). However, this study needs to be replicated in humans before we can comment on the consequences to humans.

Potential benefits of soy intake

Menopausal symptoms
Some studies suggest that increased soy consumption, especially when basal intake is low, may relieve some of the benefits of menopause (10-14). The research however is still equivocal (15-17).

Osteoporosis
The data on the effects of soy on bone mineral density are limited, but some short-term human studies show a small protective effect at the spine (18,19). Animal studies also show that soy-rich diets prevent bone loss (20-24).

Cardiovascular disease
There is a reasonable amount of evidence to suggest that the consumption of soy reduces low-density cholesterol, especially for those with hypercholesterolaemia (the bad cholesterol which increases the risk of heart disease) (19,25-29).

Cancer
There is some animal evidence to suggest that soy intake may protect against cancers of the breast and prostate (30-34). Human studies are controversial with some studies suggesting an increased risk of breast cancer (see below) (35).

Potential risks of soy intake
An evaluation of the risk and benefits of soy products is difficult because it is dependent on the nature, timing, quantity, conditions and length of exposure to soy products and in particular phytoestrogens.

Reduction in thyroxine level in those with congenital hypothyroidism
A suggested risk of high soy consumption is a reduction in the thyroid hormone, thyroxine (36). A normally functioning thyroid will compensate for this, by stimulating thyroxine production (37). However it is possible that those with congenital hypothyroidism may be unable to increase thyroxine production. This may represent a small but susceptible sub-group of the population. Consumption of phytoestrogen supplements, or a soy-rich diet, may provide sufficient concentrations of phytoestrogens to interfere with thyroxine replacement therapy. It should be noted that no adverse effects in hypothyroid children or adults have been reported in the published literature.

Breast cancer
Despite the suggested benefits of phytoestrogens in lowering the risks of developing breast cancer, there is also evidence that suggests phytoestrogens may stimulate disease progression. Studies have shown that soy supplementation of the diet can increase the proliferative rate of breast epithelium in premenopausal women with breast disease (35). It is suggested that until further research is carried out, women with oestrogen-dependent breast disease should be cautious in supplementing their diet with phytoestrogen-rich foods or dietary supplements.

References

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