In general, when someone refers to their metabolism, they are talking about their Basal Metabolic Rate (BMR) — the amount of calories needed to sustain all the body’s operations at rest (breathing, circulating blood, maintaining temperature, adjusting hormone levels, and growing and repairing cells). Your basal metabolic rate keeps going 24/7. It’s silently burning calories even while you sleep. Energy needs for your body’s basic functions stay fairly consistent and aren’t easily changed. Your basal metabolic rate accounts for about 60 to 75 percent of the calories you burn every day.
Several factors determine your individual basal metabolic rate:
- Your body size and composition. The bodies of people who are larger or have more muscle burn more calories, even at rest.
- Your age. As you get older, the amount of muscle tends to decrease and fat accounts for more of your weight, slowing down calorie burning.
In addition to your basal metabolic rate, two other factors determine how many calories your body burns each day:
- Food processing (thermogenesis). Digesting, absorbing, transporting and storing the food you consume also takes calories. This accounts for about 10 percent of the calories used each day. For the most part, your body’s energy requirement to process food stays relatively steady and isn’t easily changed.
- Physical activity. Physical activity and exercise — such as playing tennis, walking to the store, chasing after the dog and any other movement — account for the rest of the calories your body burns up each day. Physical activity is by far the most variable of the factors that determine how many calories you burn each day.
Body Size and Composition
The strongest predictor of metabolism is your body composition. How much muscle tissue you have, organs, bone tissue and how much water contained in the body.
Muscle tissue at rest consumes approximately 5 calories per pound. A recovering muscle requires more energy. Depleted glycogen stores need to be refilled. Damaged muscle cells need to be repaired. All of this requires energy.
When you think about fat’s job, it’s actually to store energy. It isn’t going to be a tissue that burns a lot of calories because that would be counterproductive. However fat is not an inert tissue, it secretes proteins such as leptin and cytokines. Fat consumes approximately 2 calories per pound.
Size does matter, the bigger you are the higher your metabolism will be but it is still down to composition.
Examples: Take two people who weigh the same. However one has a higher composition of muscle tissue and lower fat tissue. The other the reverse. The person with the higher composition of muscle tissue has a higher BMR. Now take two people with the same composition of lean mass (muscle tissue, bone tissue, organs etc), however one person has a higher level of bodyfat and weighs more. The person with the extra fat tissue has a higher BMR, not lower.
A lot of people like to blame their low metabolism for their weight gain. As you can see the opposite is true, the issue is not a low metabolism, it is their eating habits. Only in rare cases do you get excessive weight gain from a medical problem that slows metabolism, such as Cushing’s syndrome or having an underactive thyroid gland (hypothyroidism). If you rely on this as an excuse, go to the doctor and get it diagnosed and treated, or cut out the excuses.
Diet Induced Thermogenesis
At its most basic level, the Thermogenic Effect is a result of your body having to consume energy in order to digest your food. Some sources of energy are less available than others, and thus require more effort to make use of in the body.
Protein is at the top of the hierarchy of macronutrients, as far as the Thermogenic Effect goes. A whopping 27% (on average) of the calories you consume from high quality protein are used in the process of digesting the protein. Most of this is attributed to the fact that the protein has to be broken down into amino acids which then can be made use of, which is a labor-intensive process intracellularly. If you were to consume 300 Calories in pure protein, the Thermogenic Effect would burn off 81 of those calories just during the act of digestion, leaving you with 219 calories. Protein is also the most significant influencing macronutrient in determining dietary satiety, or a feeling of fullness from eating. Therefore, protein is pivotal in regulating body weight because of its key role in dietary thermogenesis–related satiety.
Carbohydrates come in second place of the hierarchy. Calories consumed from carbohydrates experience a 7% (on average) Thermogenic Effect. Low glycemic index carbohydrates tend to have a slightly higher Thermogenic Effect because they are actively dispersing energy over a longer period of time. Low GI carbohydrates also tend to be high in fibre which will help your digestive system push protein through, you don’t want to eat only protein with no fibre and become constipated.
Fats are in third place of the hierarchy. They have a pretty low Thermogenic Effect of 3%, on average, meaning that the Calories you think you’re getting are, for the most part, the Calories you are getting. Fat is the most bioavailable macronutrient, hence the low amount of energy needed to make use of it. However I don’t advise using this as a reason to cut out all fat from your diet. We need to consume essential fatty acids as our bodies cannot produce them itself.
I recommend a diet rich in high quality protein, high fibre carbohydrates and whole food plant based or fish sources of fats. Click here to download the Vitality Nutrition shopping list. I have listed everything under their macronutrient headings, I have also included oily fish under the protein section to find your essential fatty acids. Three meals a day with healthy snacks if you feel hungry between meals. Thoroughly chewing every bite of your food for optimal digestion and absorption of nutrients. Drinking 2-3 litres of water every day depending on body size and activity levels.
Avoid crash diets — those involving eating fewer than 1,200 (if you’re a woman) or 1,800 (if you’re a man) calories a day — are counterproductive for anyone hoping to lose weight. Although these diets may help you drop pounds, that comes at the expense of your metabolism. It backfires, since you can lose muscle, which in turn slows your metabolism. If you eat too little, hormones adjust, the metabolism slows down below normal to help the body conserve what it has so it doesn’t lose as much as expected. The final result is your body burns fewer calories and gains weight faster than before the diet. This starvation technique can be used by those wanting to gain weight. So if losing weight is your goal, be mindful you don’t eat too little.
While you don’t have much control over the speed of your BMR, you can control how many calories you burn through your level of physical activity. The more active you are, the more calories you burn. In fact, some people who are said to have a fast metabolism are probably just more active — and maybe even more fidgety — than others.
You can burn more calories with:
- Lifestyle activities. Any extra movement helps burn calories. Look for ways to walk and move around a few minutes more each day than the day before. Taking the stairs more often and parking farther away from where you are going are simple ways to burn more calories. Even activities such as gardening, washing your car and housework burn calories.
- Aerobic exercise. Aerobic exercise includes activities such as walking, bicycling and swimming. As a general goal, include at least 30 minutes of physical activity in your daily routine. If you want to lose weight or meet specific fitness goals, you may need to increase the time you spend on physical activity even more. If you can’t set aside time for a longer workout, try 10-minute chunks of activity throughout the day. Remember, the more active you are, the greater the benefits.
- Strength training. Strength training exercises, such as weightlifting, are important because they help counteract muscle loss associated with aging. Barre fitness, Pilates and yoga are all great strength builders which don’t place too much stress on the body. After a session of strength training, muscles are activated all over your body, raising your average daily metabolic rate.
As we age, our metabolisms do slow down. Typically, we use a number like 20%—25% [to describe how much your metabolism decreases] from the time you’re 22 to the time you’re 75 or so. So if you had a BMR of 1,500 calories at age 20, then at age 75 your BMR may be 1,200 calories.
Part of the decline in metabolic rate is hormonal. Your hormones aren’t as geared up as they once were when you were younger. But if you’re able to preserve your muscle mass, that will help offset the drop somewhat. And remember, fat-free mass is the greatest predictor of metabolic rate. Bone tissue, muscle tissue etc.
When trying to lose weight, you may hit the dreaded sticking point — when the scale won’t budge, your clothes aren’t getting looser and frustrations begin to rise. Your body is going to make adjustments to protect it’s energy reserves. At some point you come back to what we call energy equilibrium — energy intake is equal to your energy output — and you stop losing weight. That’s the sticking point or plateau a lot of people talk about. Ultimately, the metabolism wants to maintain balance and, in the grand scheme of things, that’s a function that actually makes a lot of sense.
If losing more weight is your goal, It’s the perfect time to re-evaluate your eating and exercise plan. You’ll have to either exercise more or restrict your calories more, but be wary — if you’re already at a healthy weight, be honest with yourself in analyzing whether you truly need to push to lose even more. There’s no viable reason to take your weight loss to the extreme.
Don’t look to dietary supplements for help in burning calories or weight loss. Products that claim to speed up your metabolism are often more hype than help, and some may cause undesirable or even dangerous side effects. Some dietary supplement manufacturers aren’t required to prove that their products are safe or effective, so view these products with caution and skepticism, and always let your doctors know about any supplements you take.
There’s no magical way to lose weight. It comes down to physical activity and diet. Take in fewer calories than you burn, and you lose weight. But if you’re worried about your metabolism or you can’t seem to lose excess weight despite diet and exercise, talk to your doctor.
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