- Proteins are macronutrients that are our body’s building blocks and crucial for strong muscles, organs, the blood and immune systems as well as very helpful in weight control.
- Protein from plant sources may be incomplete and may not fulfill requirement for essential amino acids in the diet.
- The primary cause of death in underdeveloped countries is related to too little protein, a condition called protein-calorie malnutrition (PCM).
Proteins are a macronutrients that consist of nitrogen containing molecules called amino acids which are essential for all living organisms. The more than 2 million proteins required for life are made up of amino acids.
Complete, incomplete, complementary
Those amino acids that cannot be synthesized are called essential amino acids and must be supplied by diet. The term complete protein refers to any protein that contains all essential amino acid building blocks. There are 20 different protein building blocks, or amino acids and the nine that the body can’t produce on its own that are considered essential amino acids. Dairy, fish, meat and eggs usually contain all of the essential amino acids and so are considered sources of complete proteins. Dietary protein from plants sources include: grains, fruits, vegetables, and legumes (legume family includes beans, peas, lentils, peanuts, and soybeans) and often lack at least one of the essential amino acids and are considered incomplete proteins. These foods, when eaten in combination, however, can fulfill all protein requirements for optimal growth and development.
Vegetables and grain products such as wheat bread, pasta, barley, and rice contain minimal amounts of protein. Legumes and whole grains are considered to be complementary sources of protein, that is, when taken together they provide all essential amino acids that a required for health. Examples of common plant-based meals (combinations) that contain all of the essential amino acids include: peanut butter and whole wheat bread; brown rice and beans, refried beans with wheat or corn tortillas, cornbread and pinto beans, falafel and whole wheat pita.
The Recommended Daily Allowance (RDA) for protein is 0.4–0.5 grams per pound of body weight for a healthy adult. For a 160 pound healthy male, that would be 64–80 grams of protein per day. The Institute of Medicine also sets a wide range for acceptable protein intake—anywhere from 10 to 35% of calories each day. Beyond that, there’s relatively little solid information on the ideal amount of protein in the diet or the healthiest target for calories contributed by protein. More protein may be required to maintain or build lean body mass in athletes and in persons with certain chronic diseases. On the other hand, too little dietary protein, a condition called protein-calorie malnutrition (PCM) represents a major public health concern. Protein malnutrition can lead to life-threatening medical conditions known as marasmus and kwashiorkor.
The lack of adequate protein causes a break down of the body’s muscle (increased muscle catabolism) in order to provide adequate energy. Lack of protein (protein malnutrition) can result in infant growth failure, loss of muscle mass, decreased immunity, weakening of the heart and respiratory system, and death. In 2000, the World Health Organization (WHO) estimated that about one in three children in developing countries (nearly 200 million children) suffered from malnourishment. In addition, an estimated 149.6 million children younger than 5 years are malnourished when measured in terms of low body weight. Incredibly, about half the children from south Asia and eastern Africa have growth retardation due to protein-energy malnutrition. Approximately 50% of the 10 million deaths each year in developing countries occurs because of malnutrition in children younger than 5 years.
Protein malnutrition is not just a developing world problem. In a survey focusing on low-income areas of the United States, 22-35% of children aged 2-6 years were below the 15th percentile for weight. Another survey showed that 11% of children in low-income areas had height-for-age measurements below the 5th percentile. Malnutrition is often under diagnosed or misdiagnosed in United States. For example, in hospitalized elderly persons, as many as half are undernourished and up to 85% of nursing home elderly persons are undernourished.
Gout and kidney disease
Gout, a painful arthritic condition related to too much uric acid in the body may directly relate to an increase in production of uric acid or the failure of the kidneys to eliminate it. Excess uric acid crystals can form as a result of high uric acid (called hyperuricemia) and may result in a gout attack. High levels of uric acid may result from the breakdown of purines found in certain high-purine foods so for those with high levels or gout these foods require restriction. Examples of such high-purine foods includes: organ meats such as liver, sweetbreads (beef or lamb thymus or pancreas), beef kidneys, brains, game meats, and gravy. Other high purine foods include anchovies, herring, sardines, mackerel, and scallops as well as plant sources such as asparagus, dried beans peas, and mushrooms. Heavy consumption of alcohol, in the form of either beer or liquor, however, should be discouraged, as it increases serum uric acid and potentially may promote a gout flare.
Dietary protein restriction is also important in patients with chronic kidney disease (CKD). However there is no consensus on the role of dietary protein restriction in slowing progression of kidney disease and this remains controversial. For those with the more advanced levels of kidney disease (Stage IV or higher) a restriction of dietary protein to about 10% of calories is generally recommended. Common in those with more significant kidney disease is the problem of too much phosphorus -a mineral found in many protein sources. The mineral phosphorous is detrimental in kidney diseases and blood levels of phosphorus may build up as kidney failure progresses. A reduction in those high protein foods rich in phosphorus is typically needed in advanced disease. Foods high in protein and phosphorus include: milk, yogurt, cheese, dried beans and peas, nuts and seeds, peanut butter and some soy products. Chronic kidney diseases are relatively common and affect at least 10% of the population or about 20 million US adults -most Americans with CKD remain undiagnosed.
There is growing evidence that high-protein food choices do play a role in health—and that eating healthy protein sources like fish, chicken, beans, or nuts in place of red meat (including processed red meat) can lower the risk of several diseases and premature death and improve the chance for an optimized weight.
Counting calories is not the best strategy for maintaining an ideal weight or for losing weight. The total dietary pattern as noted in other posts -or said in another way, the combination of foods wins at the end of the day. Protein is an important piece of a healthy dietary pattern and some meat, fish, dairy, healthy fruits and vegetables as found in a Mediterranean pattern are part of an ideal diet.
Dietary proteins influence body weight by affecting different targets important for body weight regulation. Protein is among those nutrients that provide a feeling of of fullness (or satiety). This sense of fullness is an important part of weight control and can help to restrict added calories.
Researchers at Harvard School of Public Health followed the diet and lifestyle habits of 120,000 men and women for up to 20 years, looking at how nutrition might influence health and how small changes contributed to weight gain over time. One study showed that eating approximately one daily serving of beans, chickpeas, lentils or peas can increase fullness, which may lead to better weight management and weight loss. Clinical studies have found that more protein during dietary treatment of obesity results in greater weight loss compared to diets with lower amounts of protein. When comparing two high-quality protein sources, such as beef and soy, the type of protein consumed had very little effect on appetite control and subsequent food intake. This makes the case that plant or meat sources may be used as equivalents when developing higher-protein meals. (Douglas, SM et al. Consuming Beef vs. Soy Protein Has Little Effect on Appetite, Satiety, and Food Intake in Healthy Adults J. Nutr. 2015 145:1010-1016)
Improving the body’s energy expenditure is another important piece of understanding weight control. Some macronutrients such as proteins compared to fats or carbohydrates can significantly improve energy expenditure (called thermogenesis).
The concept of diet-induced thermogenesis is important and this process is highest for protein compared to any other macronutrient. Thermogenesis increases most significantly by 20-30% after protein ingestion and 5-10% after carbohydrates and only 0-5% after a fat meal. Thermogeneisis is one component of our daily energy expenditure that also includes the basal metabolic rate and the energy cost of physical activity. The increase in metabolism related to nutrients (over the basal metabolic rate) is considered the “thermic effect” of food or dietary thermogenesis.
Protein is obviously important but remember to consider its source. Lean red meat has a different nutritional profile and health effect compared to processed meats. One investigation followed 120,000 men and women in the Nurses’ Health Study and Health Professionals Follow-Up Study for more than two decades and has led to a number of important observations. Processed red meat is strongly linked the risk of death due to heart disease. For every additional 1.5 ounce serving of processed red meat consumed each day (that is about one hot dog or two strips of bacon) there was a 20% increase in the risk of death due to heart disease. Reducing processed red meat consumption can save lives and a more recent study published August, 2016 of more than 131,000 women and men from the Nurses’ Health Study and Health Professionals Follow-up Study followed for more than 30 years reinforces this message. A higher intake of processed red meat (such as hot dogs, salami and bacon) (and not protein from fisf or poultry) compared to high protein diets from vegetable sources was associated with a higher risk of death particularly for those with at least one less than optimal lifestyle factor such as a sedentary lifestyle, smoking, excessive alcohol use or obesity (Song, M et al, JAMA Internal Medicine, 2016).
Protein quality matters more than protein quantity when it comes to diabetes risk. A 20-year study that looked at the relationship between low-carbohydrate diets and type 2 diabetes in women. Those who ate a low-carbohydrate diets that was high in vegetable sources of fat and protein modestly reduced the risk of type 2 diabetes. But low-carbohydrate diets that were high in animal sources of protein or fat did not show this benefit. Another recent found that a diet high in red meat and particularly with processed red meat, the risk of type 2 diabetes was significantly higher compared to those who rarely ate red or processed meat. For each additional serving a day of red meat or processed red meat the diabetes risk increased. The frequent consumption of processed meat showed a stunning 32% increased diabetes and substituting one serving of nuts, low-fat dairy products, or whole grains for a serving of red meat each day lowered the risk of developing type 2 diabetes from 16 to 35 percent.
The associations between protein and cancer is ongoing and again data has accumulated that the issue is of protein quality. Frequent eating of red and processed meats is strongly associated with an increased risk of colon cancer in a number of studies. The World Health Organization (WHO) International Agency for Research on Cancer (IARC) announced in 2015 that consumption of processed meat is “carcinogenic to humans,” and that consumption of red meat is “probably carcinogenic to humans.” The IARC Working Group, comprised of 22 scientists from ten countries, evaluated over 800 studies. Note the same advisory “carcinogenic to humans” is found for cigarettes.
The Nurse’s Health Study and the Health Professionals Follow-Up Study showed that every additional serving per day of red meat or processed red meat was associated with a higher risk of cancer death. Processed meat was the worst offender with a 16% increased death risk compared to that with red meat at 10%. People should reduce overall consumption of red meat and processed meat.
The bones are about 50% protein by volume and the issue of dietary protein as a good or bad actor in bone health has been controversial. Some studies suggest that increasing protein increases risk of fractures and others have found that high-protein diets increased bone-mineral density. What we do know is that protein digestion breaks down protein into acidic chemicals.
For example, meat and eggs have a lot of sulphur-containing amino acids (more than grains and beans) and when digested can form sulphuric acid. The body normally buffers this excessive acid with calcium compounds in order to maintain a normal acid-base (pH) balance. It has been proposed that high dietary protein may wind up leaching calcium from the bones (our largest reservoir of calcium) and increase the risk of osteoporosis.
Many of the early nutrition studies found an increased amount of urinary calcium levels with higher dietary protein but many failed to consider that this might not be the result of calcium leached from bones but due to an increased absorption of dietary calcium. It is also possible that for those eating more fruits and vegetables with adequate dietary calcium that this may provide adequate “buffering” capability to maintain pH balance. Despite a widely held belief that high-protein diets (especially diets high in animal protein) result in bone resorption and increased urinary calcium, many studies show the opposite: higher protein diets associated with greater bone mass and fewer fractures when calcium intake is adequate.
The Nurses’ Health Study on the other hand, did demonstrate that a high protein diet (more than 95 grams per day) compared to a more moderate protein diet (less than 68 grams) were 20 percent more likely to have broken a wrist over a 12-year period. (Feskanich, D., et al., Protein consumption and bone fractures in women. Am J Epidemiol, 1996. 143(5): p. 472-9). This area of research is still controversial and the findings have not been consistent; a rule of thumb: moderation in all things and especially in nutrition. A bigger concern should be focused on increasing the intake of alkalinizing fruits and vegetables rather than reducing protein sources.
Specific protein-rich foods like fish, nuts, eggs, cheese and yogurt to prevent weight gain must be part of mindful eating with the avoidance of refined grains, starches, and sugars.
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Song, M et al. Association of Animal and Plant Protein Intake With All-cause-Specific Mortality. JAMA Int Med. 2016