When we're young our stomachs are bottomless, our metabolisms are quick and our energy intake is matched to our growth.
However, as we get older, change occurs in every part of our bodies, including our nutrient and energy requirements.
"As we age, our bodies change -- as well as our focus, our motivation, our activity habits and our abilities," Robbie Clark, dietitian and sports nutritionist, told The Huffington Post Australia.
"Additionally, our energy and nutrient requirements and needs are different at all different stages of our life cycle, so 'eating for our age' relates to making sure we meet these requirements to achieve and maintain optimal health."
In regards to energy and nutritional needs and metabolism, the main changes that occur as we age are an increase in fat mass and a decrease in metabolism and muscle mass. For this reason, it's important to adjust our diets accordingly.
The challenge while eating less overall is to eat more nutrient-rich foods, such as fruits, vegetables, whole grains, nuts, beans, fish, low-fat dairy products and lean cuts of meat.
"As we age, we tend not to be as active and we are more prone to putting on fat mass and losing lean muscle mass, all of which contributes to our metabolism declining or slowing down," Clark said.
"Because of this reason, our total energy requirements decrease as we age as well, which is also to avoid excess fat gain. However, certain nutrient requirements increase as we age since we are at greater risk of nutrient deficiencies and certain chronic health conditions, and our bodies become less efficient at absorbing specific nutrients.
"The challenge while eating less overall is to eat more nutrient-rich foods, such as fruits, vegetables, whole grains, nuts, beans, fish, low-fat dairy products and lean cuts of meat."
Here's a rundown on the different dietary requirements during our lifetime.
"Through adolescence and our early teenage years, our bodies go through a significant growth spurt. To support the growth and development properly, this stage requires plenty of kilojoules and nutrients," Clark told HuffPost Australia.
"During this time nutrients such as protein, calcium and iron are particularly important. Hunger is also likely to increase since the body is growing, so it's important to choose foods wisely to avoid excess weight gain."
Carbohydrate intake is also important during adolescence since carbohydrate is the main nutrient to provide energy to bodily cells, particularly the brain, for growth and development, Clark added.
Adulthood and midlife
As we enter adulthood, the majority of our body's growth and development will be over. However, we still need to ensure we're getting enough essential nutrients by eating a wide variety of fresh fruit and veggies, whole grains, lean protein, healthy fats and legumes.
"We can now shift our focus to nutrition and maintaining a physically active and healthy lifestyle to reduce our risk of chronic health conditions," Clark said.
"Through most of our adult years, our energy and nutrient requirements don't tend to change that much, except for a couple of populations groups. Besides gender, the groups include pregnancy, breastfeeding, athletes and chronically ill. These groups tend to have higher energy and nutrient requirements to support the extra energy demands on the body."
During pregnancy and lactation, Clark said it's important to note that a woman's carbohydrate needs are increased.
Mature adulthood and over
As we move beyond our 50s, our energy demands decrease and, as a result, we need to make adjustments to our diet to meet these needs.
"This means decreasing our energy intake but keeping our food choices nutrient dense to make sure we are getting the most from our food to support our bones, muscles and organs," Clark told HuffPost Australia.
"During these years, fibre intake is particularly important as bowel cancer risk increases after the age of 40. Calcium is also very important to reduce risk of osteoporosis and bone fractures and breaks. Protein intake should be high to help preserve lean muscle mass, and fat intake (particularly saturated fat) should be reduced to help reduce risk of weight gain, cardiovascular disease or type 2 diabetes."
According to Clark, carbohydrate intake for elderly people depends on each individual as this group is at risk of both malnutrition and obesity.
"While a high carbohydrate diet for this population group is recommended for prevention of weight gain and obesity and to optimise fibre intake, it should be recognised that some individuals may need diets higher in energy density (for example, fats) in order to prevent malnutrition," he said.
Nutrition aside, does our age also affect the way we should exercise? According to Clark, it certainly does.
Weight-bearing exercise, such as walking or weight training, is the best type of exercise for maintenance of bone mass.
"Ageing can have an effect on our joints, muscles and bones. Therefore, it is important to pick the right type of exercises for you that your body can withstand," he said.
"Resistance or strength training is particularly important as adults and even more so as we age. The reason being is that strength training can help maintain or increase lean muscle mass, which is important as we age to reduce the risk of falls, osteoporosis, bone fractures and breaks.
"Weight-bearing exercise, such as walking or weight training, is the best type of exercise for maintenance of bone mass. As we get older, balance and coordination exercises, such as tai chi, can help reduce the risk of falls, and stretching is a great way to help maintain joint flexibility."
For those who are able, exercising most days of the week for at least 30 minutes in one session is considered to be preferable.
"Some people may choose to do more or train longer. In any case, it's important to make sure that your body gets the recovery it needs through proper rest and nutrition," Clark told HuffPost Australia.
While we may think older people are more likely to sustain injuries while exercising, according to Clark it's usually younger people who injure themselves.
"When we are younger we are more likely to push ourselves harder to our limits. As a result, we may be at higher risk of exercise-related injuries," he said.
"Younger people tend to have more energy as well so they may exercise or train for longer periods of time. If this is the case, it's very important to keep the junior athlete well hydrated as the body's thermoregulation system is still developing and provide good nutrition to support muscle growth and recovery."