What are macros? A beginner's guide to the three nutrients that make up every meal.

01. So what is a macro, exactly?

"Macro" is short for macronutrient. The word literally means a nutrient your body needs in large amounts. There are only three of them: protein, carbohydrates and fat.[2] Every single thing you eat or drink (apart from water and alcohol) is some combination of these three. A chicken breast is mostly protein with a little fat. A piece of bread is mostly carbohydrate. Olive oil is pure fat. A bowl of pasta with chicken and parmesan is all three.

They are called "macro" to distinguish them from micronutrients, which are vitamins and minerals. You need micros in tiny amounts measured in milligrams or micrograms. You need macros in amounts measured in grams, dozens or hundreds of grams a day.[2]

The reason macros matter so much is simple. They are the only things in food that supply your body with energy, also known as calories. Vitamins and minerals do not. Water does not. Fibre does not contribute much.[1] If you understand the three macros, you understand 100% of where the energy in your diet comes from.

02. The three macros, one at a time.

Protein

Protein is the body's building material. Muscles, skin, hair, fingernails, organ tissue, enzymes, hormones and antibodies are all made from protein.[3] When you eat a steak or a bowl of lentils, your body breaks the protein down into smaller units called amino acids and then reassembles those amino acids into whatever your body currently needs.

There are 20 different amino acids that humans use. Nine of them are called essential amino acids because your body cannot make them and must get them from food. Those nine are histidine, isoleucine, leucine, lysine, methionine, phenylalanine, threonine, tryptophan and valine.[4] Foods that contain all nine in good amounts are called complete proteins, and they include meat, fish, eggs, dairy, soy and quinoa. Most other plant foods are missing one or two, which is why a varied plant-based diet matters if you do not eat animal products.[5]

The current government recommendation (the RDA) is 0.8g of protein per kilogram of body weight per day. That figure was set decades ago for young, healthy adults and is now widely considered the minimum to prevent deficiency, not the optimal amount for health.[6] In Australia, the NHMRC sets a similar Recommended Dietary Intake of 0.84g per kg for adult men and 0.75g per kg for adult women aged 19 to 70, increasing to 1.07g per kg for men and 0.94g per kg for women over 70.[16] More on this when we get to the over-40 part.

Carbohydrates

Carbohydrates are your body's quickest, easiest source of fuel. When you eat anything from rice and bread to fruit and vegetables, your body breaks the carbs down into glucose, a simple sugar that circulates in your bloodstream and powers your brain, your muscles and almost every cell you have.[1][7]

People often talk about "good carbs" and "bad carbs", which is loose language for a real distinction. Complex carbohydrates like oats, whole grains, beans, vegetables and most fruit come bundled with fibre, which slows the release of glucose into your blood and keeps you full for longer. Simple carbohydrates like white sugar, soft drinks, lollies and most ultra-processed snacks hit your bloodstream almost immediately, give you a short energy spike, and then drop you back down.[7]

One special carbohydrate worth a separate mention is fibre. Fibre is the part of plant foods your body cannot digest. It does not give you calories the way other carbs do, but it feeds your gut bacteria, slows digestion, lowers cholesterol and helps with bowel regularity.[8] The Institute of Medicine recommends 25g of fibre per day for women and 38g for men under 50, and 21g and 30g respectively for women and men over 50.[8] The Australian NHMRC sets a similar Adequate Intake of 25g per day for adult women and 30g for adult men.[17] Most adults in both countries consume only about half that.[8]

Fat

For decades fat was unfairly painted as the villain of the food world. The current science is much kinder. Dietary fat is essential. Your body needs it to absorb fat-soluble vitamins (A, D, E and K), to produce hormones including testosterone and oestrogen, to build cell membranes, and to insulate your nervous system.[2][3]

The general buckets are unsaturated fats (in olive oil, avocados, nuts, seeds and oily fish), which are linked to better heart health, and saturated fats (in butter, fatty cuts of meat and full-fat dairy), which most major health bodies recommend keeping moderate. The Heart Foundation Australia advises a heart healthy eating pattern that emphasises monounsaturated and polyunsaturated fats from foods like nuts, seeds, avocados, olives and oily fish, while limiting saturated and trans fats.[18] Trans fats, the artificial kind found in some old-school margarines and packaged baked goods, are the only fats with no nutritional upside and are now banned or restricted in many countries.[9]

Fat is the most energy-dense macro by a wide margin. 9 calories per gram is more than double what you get from protein or carbs. That is why a tablespoon of olive oil contains around 120 calories while a tablespoon of honey, which is pure carbohydrate, has around 60. It also means small portions of fat add up quickly, which is worth knowing before you pour an extra generous glug on your salad.

03. Calories and macros, what is the difference?

This is where the penny usually drops for people new to nutrition.

A calorie is a unit of energy. Specifically, it is the amount of energy needed to raise the temperature of one kilogram of water by one degree Celsius. When a food label says a meal contains 500 calories, it is telling you the total amount of fuel that meal will supply to your body.

But "500 calories" is silent on where those calories come from. Five hundred calories from a salmon fillet and a sweet potato will behave very differently in your body than 500 calories from a can of soft drink and a packet of chips, even though both add the same number to your daily total.

Macros are how you describe the composition. If you know a meal contains 30g of protein, 40g of carbs and 15g of fat, you can do the maths yourself: (30 × 4) + (40 × 4) + (15 × 9) = 415 calories. The macros explain the calories.[1]

Most government health bodies publish ranges for how much of your daily calories should come from each macro. The Institute of Medicine's Acceptable Macronutrient Distribution Ranges (AMDR) are: protein 10 to 35%, fat 20 to 35%, carbohydrates 45 to 65%.[10] These are deliberately wide because there is no single right ratio for every body. Where you land inside those ranges depends on your goals, your activity level, and as we will see in a moment, your age.

04. Why tracking macros works (according to the research).

You do not have to track anything to be healthy. Plenty of people eat well their whole lives without weighing a single piece of broccoli. But the research on people who do track is strikingly consistent.

Self-monitoring doubles weight loss. A 2008 study by Hollis and colleagues at Kaiser Permanente followed roughly 1,700 overweight adults for six months. The single strongest predictor of who lost weight was how often they kept a food record. Participants who tracked their food daily lost about twice as much weight as those who kept no records at all.[11]

The pattern holds across dozens of studies. A 2011 systematic review in the Journal of the American Dietetic Association looked at 22 separate studies of dietary self-monitoring. The authors concluded that more frequent tracking was "consistently and significantly" associated with weight loss success.[12]

You do not need to track perfectly. A 2024 University of Florida study found that tracking food at least three days a week was enough to support long-term weight loss maintenance, with even better results at five to six days.[13]

Why does it work? Almost certainly because of awareness. Most people genuinely do not know what is in their food, and the act of writing it down forces a moment of honesty. The salad dressing turns out to have 200 calories. The "small handful" of nuts is actually 350. The afternoon biscuit you forgot about is real and it counts.

There is also a specific reason tracking macros rather than just calories gives an extra advantage: protein behaves differently from the other two macros in your body. It is more filling per calorie, and it actually costs your body energy to digest. This is called the thermic effect of food:

That means 100 calories of chicken breast effectively delivers fewer "net" calories to your body than 100 calories of butter, because your body works harder to process it.[14] Combine that with the fact that protein is more filling than the other two, and you get the most consistent finding in modern nutrition research: diets higher in protein tend to produce more weight loss and better muscle retention than lower-protein diets at the same calorie level.[14]

Calorie counting on its own cannot capture any of this. Macro tracking can.

05. Why this matters more after 40.

If you are under 30, healthy and eating intuitively, the case for tracking macros is mostly about goals: losing weight, building muscle, performing in a sport. After 40 the case becomes more about protection.

Three things start to shift in your body once you cross 40, and all three are addressable with the right macros:

You lose muscle slowly but steadily. Adults lose roughly 3 to 8% of their muscle mass per decade after 40, with the rate accelerating after 60. Muscle is what burns calories at rest, keeps you strong, protects your joints and reduces fall risk. Losing it is the single biggest physiological change that makes eating the same way you did at 30 stop working in your 40s.

Your body becomes less efficient at building muscle from protein. Researchers call this anabolic resistance. The 0.8g/kg protein RDA was set for young adults and is now widely recognised as too low for adults over 40 who want to preserve muscle. Newer research from Frontiers in Nutrition and other sources recommends at least 1.2g per kg of body weight, with 1.6g/kg as the upper end of the evidence-based range for active adults.[6]

Body composition shifts toward more fat and less lean tissue, even at the same weight. This is why the bathroom scale can read the same number it did ten years ago while your clothes fit differently. Tracking macros, particularly hitting a protein target, is one of the few interventions shown to slow this drift.[6]

You do not need to overhaul your diet. You need to know what you are eating, and then make sure protein is high enough. That is the practical case for paying attention to macros after 40. Once you can see your numbers, the rest gets easier.

06. So how do you actually do this?

If you are sold on the idea and want to start, the workflow is straightforward and free:

• Calculate your daily targets. Use a calculator that accounts for your age, sex, weight, height and activity. The macro calculator on this site is built for adults over 40 and sets protein at 1.6g per kg of body weight, based on the research above.
• Find out what is in your food. Either read nutrition labels or use a reference like our food macros guide, which lists protein, carbs, fat and fibre for 161 common foods sourced from the USDA database.
• Log what you eat for a week. Use a spreadsheet, a notebook or an app. The goal is awareness, not perfection. The research is clear that even imperfect tracking three or four days a week is enough to move the needle.[13]
• Adjust based on what you see. Most people discover they are eating less protein than they thought, more fat than they thought, and more total calories than they thought. Once you can see the numbers, you can make small, sustainable changes instead of guessing.

You do not need to track forever. Many people find that after a few weeks they have learned what an adequate amount of protein looks like on a plate and they can stop logging entirely while keeping the habits. Some people track in seasons (during fat loss phases, before a holiday) and not in others. There is no rule.

07. When tracking is not a good idea.

Honesty matters here. Tracking macros is a tool, not a moral good, and it is not right for everyone.

Other situations where tracking may not be the right tool:

• You are pregnant or breastfeeding (your calorie and nutrient needs are different, and intuitive eating is generally recommended).
• You have a complex medical condition affecting nutrition (chronic kidney disease, diabetes on insulin, malabsorption disorders). Work with a registered dietitian instead.
• The numbers make you anxious rather than informed. If logging food makes you feel worse about yourself or your meals, stop. The goal is awareness, never guilt.

For most healthy adults over 40, however, paying attention to macros is one of the highest-leverage things you can do for your health, your body composition and your energy. The research is robust, the cost is zero, and the only commitment is a few minutes a day for as long as you want to keep doing it.

08. The takeaway.

Macros are not complicated. They are just the three nutrients that supply every calorie in your diet: protein for repair and muscle, carbohydrates for fuel, fat for hormones and absorption. The reason they are worth knowing about is that calories alone do not tell you the full story of how a meal will behave in your body. Macros do.

For adults over 40, the case is stronger again. Muscle is harder to keep, protein is more important, and your body has less margin for guesswork than it used to. You do not need to be perfect. You need to be informed.