INTRODUCTION
Although eating is an activity everyone should know a great deal about, many persons fail to eat a nutritionally balanced diet and do not take advantage of the many natural food sources that not only can provide necessary nutrients, but can also help maintain health and promote a more successful aging process. Many persons eat to excess or fail to consume basic requirements necessary for health. Malnutrition is not something observed only in third-world countries. In addition to a necessary amount of proteins, carbohydrates, and fats, we must ensure an adequate intake of vitamins, minerals, and trace elements. The elderly are particularly prone to developing protein-calorie malnutrition, as well as many other vitamin and mineral deficiencies. This may result from problems that occur with increased frequency later in life, such as poor dentition, loss of taste, difficulty swallowing, malabsorption, or drug-nutrient interaction. An inability to obtain the necessary fresh foods, as may occur during the wintertime or if someone is dependent on others to shop for him or her, may also predispose to nutritional inadequacies. Nonperishable foods may contain high concentrations of sodium and nitrates and may lack vitamins due to processing methods. A person eating less than 1500 calories a day may lack the simple variety of foods necessary to ensure a proper intake of vitamins; this is not uncommon during later life, and a daily vitamin can add insurance to the diet where doubt exists.
What is most worrisome is the growing number of individuals who are obese. Over 30% of the U.S. population is currently considered to be overweight and at risk of developing obesity-associated problems later in life, such as heart disease, diabetes, arthritis, sleep apnea, strokes, and hypertension, among others. A healthy diet must start early in life when patterns of eating become ingrained and tastes and preferences acquired. Childhood obesity is on the rise, and families would be wise to consider their diets in relation to all members of the family unit. Portion size has increased in recent decades, and fast food has become a more staple part of the diet, with more children growing up in homes with their only parent or both parents working. Snack foods have proliferated with high concentrations of “refined” sugar; soda and fruit drinks have frequently replaced healthier foods.
While food labels are now required, it often takes considerable knowledge or even an advanced degree to understand the details provided. The number of portions listed on a label, even for foods contained in what appears to be a single-serving package, may be missed by the nonskilled reader or someone who cannot read the small print. Caloric content is often much higher than what one had thought. Number of grams of fiber listed may be based on a 100-gram portion. The casual reader may confuse the number listed with the actual amount contained in what he or she will eat in a single serving: 100 grams of puffed wheat is clearly different than 100 grams of bran buds, for example.
Certain foods may have protective effects against heart disease and cancer, while others may actually promote disease. Diets high in animal fat may predispose to rectal, colon, breast, and prostate cancer. The prostate cancer death rate is five times higher in the United States and in northern Europe than it is in Hong Kong, Iran, Turkey, and Japan, where diets emphasize more vegetables, grains, beans, cereals, and fruits. These foods also have been epidemiologically associated with a lower incidence of stroke. Fat also predisposes to heart disease. Conversely, diets rich in omega oils and fiber, for example, can help prevent certain age-prevalent illnesses.
The topic of nutrition and what one needs to do to ensure a more successful aging process is quite exhaustive, and a total review is beyond the scope of this article. Data concerning dietary factors and caloric intake and their role in possibly increasing lifespan remains controversial, especially in humans, and this will remain a topic for another time. This two-part article focuses on known associations between certain key dietary components and health and disease, attention to which may promote a more successful aging process. Part I discusses energy, protein, and fats, and Part II (to be published in a future issue of Clinical Geriatrics) will examine fiber, multivitamins and micronutrients, antioxidants, and calcium.
ENERGY
Every individual has a specific energy requirement in order to remain in caloric balance and remain at a certain weight. Small adjustments can be made to either increase or decrease calorigenesis in response to over- or underfeeding, with the catecholamines and thyroid hormone being mostly responsible for these variations on a day-to-day basis. We are able to increase or decrease our catecholamine turnover rate, as well as alter our ability to convert thyroxine (T4) to its more metabolically active metabolite 3, 5, 3’ triiodothyronine (T3). Genetic factors, illness, and age are just some of the factors that have been shown to be capable of altering the normal metabolic response to diet. If this change in diet becomes more of a regular occurrence, the body establishes a new set point and attempts to maintain this weight for as long as possible, once again using homeostatic mechanisms to either up- or down-regulate caloric balance. Data suggest that as we age, we have a more difficult time adjusting to this caloric variation, and thus may gain or lose weight more dramatically than when we were younger under similar circumstances.
In the 1930s, Clive McCay demonstrated that the rats in a pair-fed control group who were fed 60% of their normal diet had fewer age-prevalent diseases. This same model has been studied extensively by investigators throughout the world, with many age-associated physiological changes in rats reportedly slowed by this reduction in calorie intake. While some advocate for a similar study in humans, it appears that this apparent benefit from dietary restriction is not universal, even in all other rodent species. Some have argued that this caloric restriction is more similar to a “natural rodent diet,” and, in fact, rats kept in captivity in the laboratory being fed ad libitum around the clock is not natural and may actually prematurely age these rodents; rodents in the wild are scavengers and often go for days between meals. The laboratory model of 60% intake, or the equivalent of feeding them every other day, may be more similar to what nature intended.
Epidemiologically, the longest living humans tended to be thin when young but gained weight throughout their lives, yet never became obese. This “additional weight” might very well be protective in times of illness, when a catabolic state may result. Based on these findings, the Metropolitan Life Insurance Company tables of average weight for age were upgraded throughout the lifespan, with new goals established for optimal weight at a given age. Clearly, there must be a balance between being “too thin” and “too heavy,” as both appear to shorten one’s potential lifespan.
When calculating one’s energy expenditure, the energy expended at rest, during physical activity, and in response to one’s environment must be considered. Variables such as age, sex, muscle mass, genetics, dietary intake, temperature, and disease all are capable of influencing one’s energy requirements. Resting energy expenditure (REE) and basal metabolic rate (BMR) are terms used interchangeably and differ by less than 10% under usual conditions. It has been known for many years that BMR declines as a function of age; in 1977, however, this age-related change was found to be primarily due to age-related changes in muscle mass, and not some major metabolic change that occurred as a function of age. While the Harris-Benedict equation can be used to calculate REE, it requires a chosen cofactor that results in significant variability, and thus has limited clinical value. In general, REE is approximately 1750 kcal for men weighing 70 kg, and 1350 kcal for women weighing 58 kg. This increases to 2400 and 1850 kcal, respectively, for men and women who lead sedentary lives, and as high as 4000 and 3000 calories, respectively for men and women who are very active physically.
These numbers vary greatly, but in general are 10-20% lower for people over the age of 65, and an additional 10% lower in those over age 80. A number of diseases common during later life can impair caloric intake and ingestion of necessary nutrients for health. Whether there is an inadequate intake of calories or just protein, the immune system can be affected and infections more common. Delayed wound healing, a decline in certain neurotransmitters, as well as one’s ability to respond to changes in ambient temperature are just some of the other possible associated findings.
Individuals who have problems eating may be better served by having multiple small feedings throughout the day, with particular attention to dietary preferences and proper nutritional intake; the use of dietary supplements or vitamins should also be considered for those at risk. Nutritional counseling regarding the best way to obtain appropriate quantities of certain nutrients may be necessary, and physicians would be well served by having the name of a registered dietitian to whom they could refer patients in need. We must be able not only to identify those who are not obtaining adequate diets, but also to anticipate who is at risk. Those individuals who are depressed, recently bereaved, or have had a change in their living situation are also at high risk of becoming malnourished. Eating is a social behavior, and any situation that affects one’s customary dietary habits may have significant consequences.
PROTEIN
Both animal and plant proteins consist of approximately 20 common amino acids. The proportion of these amino acids varies as a characteristic of a given protein. Because proteins and other nitrogenous compounds are degraded and resynthesized on a regular basis, a continuous supply of dietary amino acids is required to replace these losses, even after growth has ceased.
Nine amino acids, known as “essential” amino acids, are not capable of being synthesized by the human body, and are therefore considered to be indispensable nutrients. These include histidine, leucine, isoleucine, lysine, methionine, phenylalanine, threonine, tryptophan, and valine.
The protein content of the adult body diminishes with increasing age. While longitudinal data about the relative loss of visceral compared to skeletal muscle protein are scarce, cross-sectional studies suggest that total body protein declines with age, a change that accelerates after 65 years of age.1 This accelerated decline in total body protein contributes to the age-associated loss of skeletal muscle, a process called sarcopenia. Because sarcopenia exposes the elderly to an increased risk for disability and injury, strategies to counteract a loss of skeletal muscle using nutritional interventions and exercise have been investigated. Changes in muscle mass are related to whole-body protein turnover and the protein synthesis rate.2
The current Recommended Dietary Allowance (RDA) for protein is 0.8 g/kg per day.2 Recent studies assessed the adequacy of this RDA to maintain body composition, protein metabolism, and muscle mass in older people. In a 14-week, follow-up, controlled-diet study, 10 healthy ambulatory men and women age 55-77 years were provided eucaloric diets containing 0.8g/kg per day of protein.3 Subjects in the study adapted to this level of dietary protein by maintaining their body composition and protein steady-state. There was, however, a decrease in mid-thigh muscle area consistent with metabolic accommodation and a compromise in physiological function. These authors concluded that while elderly individuals might adapt to 0.8mg/kg per day of dietary protein and achieve a steady-state, this recommended level may not be adequate to completely meet the metabolic and physiological needs of all older individuals.3
Not all studies support the recommended level of protein intake. In fact, long-term protein intake has been shown in a rodent model to increase the risk of renal glomerular sclerosis, and might also contribute to the development of osteoporosis.4,5 Therefore, it has been suggested that limiting dietary protein intake might delay the development of age-related changes in renal function.6
While many elderly persons consume adequate amounts of protein, some have a reduced appetite or altered eating patterns and consume less than the protein RDA. For this reason, numerous studies have focused on counteracting muscle loss by changing not only the quantity but also the quality of ingested proteins. The aim is to optimize protein intake through an improvement in amino acid bioavailability for muscle tissues.7 While aging is associated with changes in the metabolism and response of muscle protein to a meal, the older person’s muscle is still able to respond to amino acids, mainly essential and branched-chain amino acids (BCAAs). This likely results from the stimulatory effects of these amino acids, mainly leucine, on the initiation of muscle protein synthesis, which is still present in older individuals.8 Long-term essential amino acid supplementation may be a useful tool for the prevention and treatment of sarcopenia, particularly if excess leucine is provided.8
Since physical activity tends to decline with aging, some have argued that sarcopenia may also result from disuse rather than aging per se.1 Therefore, in addition to providing adequate proteins, investigators have explored the role of exercise, mainly strength conditioning or resistance training, to help counter the development of sarcopenia. While endurance exercise increases the oxidation of essential amino acids, strength conditioning enhances muscle size largely due to an increase in contractile proteins. Furthermore, while both aerobic and strength conditioning are highly recommended, Evans9 suggests that only strength training can stop or reverse sarcopenia. Thus, in addition to adequate protein intake, strength-conditioning exercises seem to be a realistic strategy for maintaining optimal functional status in the elderly population.
Individual protein requirements for older adults involved in resistance training may vary according to health and training regimen. Concerns have been raised as stated previously about the potential consequences of long-term, high-protein diet on renal function. Using an animal model, Anderson and Brenner4 initially postulated that excess protein intake may accelerate the decline of renal function with age. Furthermore, at least one study reported that protein restriction may prevent the age-associated decline noted in renal function.4 Nevertheless, the Committee on Military Nutrition Research has suggested that the potential adverse effects of protein intake on renal function not be considered, and recommends that there be no restriction on protein intake in healthy individuals regardless of age.10 Lucas and Heiss11 suggested an intake of 1.0-1.3 g/kg per day of protein for older adults engaged in resistance training, with attention to ensuring adequate caloric intake. Clearly, older individuals with long lifespans may be at risk of accelerated renal insufficiency and osteoporosis if they consume higher proteins in their diets; therefore, monitoring these parameters while balancing them with muscle mass appears prudent in these individuals.
While general RDAs for protein intake exist, individualized nutritional guidelines that take into account renal function, bone status, expected lifespan, and functional ability would be advantageous. Recently, the United States Department of Agriculture (USDA) and the Department of Health and Human Services jointly announced the unveiling of the website www.mypyramid.gov based on the Dietary Guidelines for Americans 2005. The site is interactive and enables one to tailor his or her diet plan based on age, gender, and activity levels. The site also provides tips on making wise choices for protein intake from the meat and bean groups. It recommends to “go lean with protein,” and favors dry beans or peas as a main dish or part of a meal. For those who choose to eat meat, the leanest beef cuts include round steaks and roasts, top loin, top sirloin, and chuck shoulder and arm roasts. The leanest pork choices include pork loin, tenderloin, center loin, and ham. Boneless skinless chicken breasts and turkey cutlets are the leanest poultry choices. The USDA also recommends eating fish more often for lunch or dinner, especially fish rich in omega-3 fatty acids, such as salmon, trout, and herring.12,13
FATS
Dietary fat has been one of the most controversial topics over the past several decades. As obesity is exponentially growing in North America, so are new “no-fat” or “low-fat” diets and foods flooding the market. In the 21st century, it has become general knowledge that obesity is associated with many health problems, especially in the aging population: heart disease, diabetes, depression, sexual dysfunction, and arthritis, just to name a few. Are the dietary fats solely to blame for the obesity epidemic and associated problems?
Digested dietary fats break down into their components, free fatty acids and monoglycerides, in order to be absorbed. In the human body, free fatty acids can be directly utilized as a source of energy by most cells; erythrocytes and nerve cells are the exception. Brain cells, however, are able to utilize ketones that are produced by fatty acid breakdown when glucose supplies are scarce. In addition to being an energy source, fats play a crucial role in soluble vitamin absorption. They are precursors of structural lipids forming the cell membrane, prostaglandins, thromboxanes, and leukotrienes. Additionally, fats are building blocks of steroid-derived hormones. While fatty acids are an important nutrient for human consumption, they are not all equal. The structure of fatty acids is composed of carbon atom chains surrounded by hydrogen atoms. The bonds between the carbon chains classify fatty acids into saturated fatty acids (SFAs), containing single bonds only; monounsaturated fatty acids (MUFAs), containing one double bond; and polyunsaturated fatty acids (PUFAs), containing more than one double bond. The PUFAs are further subdivided into omega-3 and omega-6 fatty acids, depending on the distance of the first double bond from the methylated carbon. Two of the PUFAs, linoleic (omega-6 PUFA) and linolenic (omega-3 PUFA) are considered essential fatty acids because the human body cannot synthesize them. Small amounts of these essential fatty acids must be present in our diet to maintain health (Table I).
Growing evidence shows that it is, in fact, the structure of fatty acids and the number of double bonds between carbon atoms that play a central role in the etiology of numerous chronic diseases. Various studies suggest a protective role of PUFA and MUFA, and a harmful effect of SFA in many diseases affecting the aging population. The Mediterranean diet, with its hallmark of high levels of utilization of olive oil (high in content with MUFA : PUFA=5:1), has had a pivotal role in many studies. Trichopoulou and colleagues14 suggested significant reduction in mortality among patients with known coronary heart disease who adhered to a traditional Mediterranean diet. Fito and colleagues15 studied the effect of virgin olive oil, rich in phenolic compounds, and found that it significantly decreased oxidized low-density lipoprotein (LDL) and lipid peroxide levels, as well as reduced systolic blood pressure in individuals with known coronary heart disease. In an 8.5-year follow-up study of 704 elderly patients, Solfrizzi and colleagues16 investigated the role of MUFA, PUFA, and SFA on all-cause mortality and concluded that higher MUFA intake as found in the typical Mediterranean diet increased survival; higher SFA marginally increased total mortality. The role of olive oil has also been studied in relation to hypertension in elderly subjects. Perona and colleagues17 found that a diet using virgin olive oil as its fat source was helpful in reducing the systolic pressure of treated elderly subjects with hypertension. In a meta-analysis of 17 controlled trials, Appel et al18 analyzed diet supplementation with fish oil, high in omega-3 PUFA, and concluded that 3 grams per day of omega-3 PUFA can lead to clinically significant reductions in blood pressure in individuals with untreated hypertension. In addition to examining the effect on the cardiovascular system, the effect of MUFA and PUFA was also studied in relation to several types of cancer. Wolk et al19 performed a prospective study analyzing MUFA and risk of breast cancer in a large population of Swedish women without previous history of breast cancer. They found that MUFA (olive oil) had a protective effect on the risk of breast cancer, while PUFA (vegetable oil and margarine) was significantly positively associated with an increased risk of developing invasive breast cancer.19
The effect of dietary fat on colon cancer has been addressed in many studies. Meta-analysis by Howe and colleagues20 found null association in 1997, but several newer studies have shown an association. Stoneham et al,21 in their ecological study using existing international databases, compared national levels of olive oil consumption to the difference in incidence of colorectal cancer. They found that olive oil may have a protective effect on the development of colorectal cancer by influencing secondary bile secretion patterns, while meat and fish were associated with increased risk of colorectal cancer.21 Using data from the Women’s Health Study, Lin and colleagues22 also looked at the relation of dietary fats to colorectal cancer in women. Although the study provided little support for any association between dietary fat and colorectal cancer risk, it noted that the intake of fried foods, high in trans-fats, may be associated with colorectal cancer development.22
Three very recent articles found that a low-fat dietary pattern did not significantly reduce the risk of developing invasive breast cancer, colon cancer, and cardiovascular disease in women who participated in the Women’s Health Initiative Randomized Controlled Dietary Modification Trial.23-25 Although these were large studies, the follow-up was only 8 years, and benefits of fat reduction may not have become evident within this time frame. Also, it is important to note that fats in these studies’ diet were restricted rather than a diet that encouraged certain fats, such as MUFA and PUFA. The limitation of these studies was that the intervention was likely started “too late” and was not followed long enough to see differences between groups. Fat in the diet likely has a long-term impact on cancer prevention or etiology of heart disease, and if one is to derive maximal benefit, modification should be started early in life.
Solfrizzi et al26 performed a comprehensive review of nine studies on the effect of dietary fatty acids on cognitive decline and dementia. The review found that while SFA could possibly have a negative effect on cognitive function, there was a clear reduction of cognitive decline in the population sample with high intake of omega-6 PUFA, omega-3 PUFA, MUFA, and weekly fish intake.26 The role of fatty acids has also been studied in relation to the risk of having a stroke by Iso and colleagues,27 who found that linolenic (omega-3 PUFA)—but not linoleic (omega-6 PUFA)—acid was significantly associated with reduced risk of stroke among men at high risk of cardiovascular disease. The exact role of linolenic and linoleic acids in human nutrition is still being studied. It has been suggested, however, that a diet deficient in these two essential fatty acids can lead to vision problems (linolenic deficiency) and impaired wound healing (linoleic deficiency). Although Djousse et al28 suggested that higher intakes of both linolenic and linoleic acid help decrease the risk of cardiovascular disease, others report that while higher dietary linolenic acid is inversely related to risk of coronary artery disease (CAD), higher linoleic acid intake may actually be associated with an increased rate of CAD, cancer, and inflammatory diseases.28-32
The Food and Nutrition Board’s Committee on Diet and Health recommends that the fat content in an average adult diet not exceed 30% of caloric intake, and that less than 10% of calories come from saturated fatty acids. The committee also recommends that dietary cholesterol intake should be less than 300 mg per day.2 After comprehensive review, the evidence indicates that the majority of elderly individuals’ dietary fats should come from foods rich in MUFA, such as virgin olive oil and sunflower oil. Omega-3 PUFA (linolenic acid) found in flaxseeds, flaxseed meal, hempseed oil, hempseeds, walnuts, pumpkin seeds, Brazil nuts, sesame seeds, avocados, some dark leafy green vegetables (eg, kale, spinach, purslane, mustard greens, collard greens), canola oil (cold-pressed and unrefined), soybean oil, wheat germ oil, salmon, mackerel, sardines, anchovies, albacore tuna, and other foods, should also be abundant in an elderly individual’s diet. Omega-6 PUFA (linoleic acid), found in flaxseed oil, flaxseeds, flaxseed meal, hempseed oil, hempseeds, grapeseed oil, pumpkin seeds, pine nuts, pistachio nuts, sunflower seeds (raw), olive oil, olives, borage oil, evening primrose oil, black currant seed oil, chestnut oil, chicken, and other sources should be limited to less than 7% of daily calorie intake. Dietary fats to be avoided are those rich in saturated fatty acids and trans fatty acids. Saturated fatty acids are found in coconut and palm oils, as well as in animal fats such as red meat, lard, and dairy products. Trans fatty acids are a relatively new concept. These are unsaturated fatty acids that were subjected to the process of hydrogenation with an idea to replace saturated fatty acids. Trans fatty acids are found in margarines, high-fat baked foods (doughnuts, cookies, and cakes), french fries, potato chips, corn chips, and any product whose label notes “partially hydrogenated vegetable oils.” Willett and colleagues,33 as well as many newer studies, showed that trans fatty acid, just as saturated fatty acid, contributes to the development of CAD.
An additional and very important element of dietary fat intake is the mode of preparation. High heat used in frying and cooking may destroy double bonds in MUFA and PUFA, distorting their original structure. It is, therefore, recommended to consume these foods in their raw form. When cooking, extra virgin olive oil, canola oil, or grapeseed oil is preferred, as these withstand high heat with minimal structural change.
When choosing a diet, caution is advised, as “low-fat” foods may not be low in calorie. In fact, this type of food may promote weight gain if its caloric values are not properly understood (Table II).
SUMMARY
Careful attention to diet throughout life is essential if we are to have a more successful aging process and minimize disease. How successful we age is largely determined by our genetic makeup. Nevertheless, we all have within our control the ability to lead healthier lives, and proper diet can play a key role. Physicians should incorporate questions relating to diet into medical history, and should identify and address any findings associated with either over- or undernutrition. Attention should be given to proper intake of calories, protein, fats, and the necessary nutrients, such as fiber, calcium, and vitamins and minerals, which will be discussed in Part II of this article.
The author reports no relevant financial relationships.