Metabolism - Separating Fact From Fiction

Metabolism is the process by which your body converts what you eat and drink into energy. Your metabolism refers to the collection of daily processes your body uses to keep things working efficiently. Metabolic function fuels everything you do.

The 3 main roles of your metabolism are:

  • Converting food to energy for your cells
  • Turning foods into building blocks for proteins and fats to maintain your body’s tissues
  • Eliminating waste from your body

Your body is constantly adapting to your needs. It is making energy, breaking down and rebuilding cells and tissue, and eliminating waste, which means it is extremely challenging to get an exact measurement of your actual daily metabolic needs.

This is one of the reasons why your metabolism is quite misunderstood. It often gets tossed around in dubious diet claims (boost your metabolism to burn fat), shady weight loss predications (Not eating breakfast will slow your metabolism!), and blatant lies (apple cider vinegar speeds up your metabolism).

There are 4 basics to metabolism:

  • BMR, or Basal Metabolic Rate
  • TEF, or Thermic Effect of Food
  • PA, Physical Activity Expenditure
  • NEAT, which is Non-Exercise Activity Thermogenesis.

BMR + TEF + PA + NEAT = the calories you use in a day. This is what most people equate with their ‘metabolism’.

The BMR is the number of calories that your body uses for its basic daily and living functions including heartbeat, temperature control, and brain function. BMR is the energy keeping you alive. Powering your body at rest uses between 60% and 75% of your total calories. BMR is thought to vary up to 15% between individuals.

The TEF is the number of calories your body uses to digest food. Each macronutrient (carbohydrate, protein, and fat) has a different thermic effect. Protein takes the most energy for your body to process (somewhere near 20% of its calories). Fat takes the least (around 5%). This is one of the reasons why higher-protein diets can be effective for weight loss as you are utilizing more energy to metabolize your meals.

You may be tempted to eat a protein only diet as it appears to burn more calories but Paleo principles advocate eating a variety of foods other options which provide nutrients that protein cannot. Varying your diet is also more interesting and delicious.

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The thermic effect of food is generally thought to account for around 10% (and up to 15%) of your daily caloric intake.

NEAT is anything that is not purposeful exercise, like taking a shower, standing in line, fidgeting or doing laundry. NEAT can account for a significant number of calories per day whereas actual exercise accounts for a very small percentage of activity calories burned.

Your BMR Is Unique

Your BMR is determined and governed by many factors:

Muscle Mass.

The more muscle you have, the higher your BMR. Some people build muscle easier, some people have more muscle (men naturally have higher BMRs than women for this very reason), which can make a difference between your BMR and someone else’s regardless of exercise level. Muscles require about 7 calories/pound of energy per day. Those with more muscle mass will naturally have higher BMR’s. This is often the reason men tend to lose weight quicker than women.

As you age, you lose muscle mass, often due to. Being more sedentary, leading you to believe that metabolism decreases with age. When following a Paleo lifestyle and including exercise in your program, this need not be the case

Fat Mass.

A less important contributor to BMR is adipose tissue (fat). Fat burns only around 2 calories/pound, but this effect can add up quickly in people who have a lot of it. If a 250-pound person loses 100 pounds, which amounts to 200 calories a day that is no longer needed and needs to be accounted for in the diet.

Food Intake.

In the long term, an extreme starvation causes your metabolism to slow in response, because your body is conserving energy in an attempt to help you stay alive. On the other hand, overeating will raise your metabolic rate (although not enough to burn all the extra calories).


Your genes play a role in everything about you. BMR is influenced by genetics, but your genetics to not fully determine your BMR. As with many genes, lifestyle factors play a huge role in their expression.

Metabolism is much, much more complicated than some people genetically having a “fast or slow metabolism. It is not entirely under your control, and a lot of the advice on how to raise your metabolic rate either produces such a small benefit that it barely matters or produces no benefit at all.


Studies suggest that people who get insufficient or poor-quality sleep may have a reduced metabolism.


Thyroid hormone levels in particular can influence BMR, as can your reproductive and stress hormone levels.

Can You Boost Your Metabolism?

Cayenne pepper and apple cider vinegar will not boost your metabolism!

The only thing known to effectively boost metabolism for the long-term is exercise. The more lean body mass you have, the more calories you will burn at rest (this is a higher BMR). A pound of muscle burns around 7 calories a day at rest; a pound of fat, just 2. This may not seem like a huge difference, but it is enough to make an impact over the long-term.

A very large meal can actually increase your TEF short-term. However, again, this is probably not significant enough to reduce many of the other effects of over-eating.

Metabolism Myths And Truths

Eating Many Small Meals To Boost Metabolism.

Eating more frequently may actually cause some people to eat more and eating more or less often makes little difference in terms of BMR and fat loss. Do whatever works best for you. Eating may increase your TEF short-term, but this happens in proportion to the number of calories you eat. Eating six times a day will give you six mini-boosts; eating the same number of calories in two meals will give you two larger boosts that are exactly equivalent to the six mini-boosts.

When eating whole, real, nutrient dense foods (the Paleo diet!), hunger is often satiated and the need for snacking disappears

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Skipping Breakfast Slows Metabolism.

Eating breakfast has been associated with weight loss in some individuals because breakfast-eaters may be more likely to be active, but as far as actual slowing of the metabolism, there is no convincing evidence.  

Eat breakfast if you find that it helps you eat less later in the day, and of course, if you are hungry when you get up. If you are not a breakfast eater, you are following an intermittent fasting protocol and you don’t feel that it impacts your food intake or your physical and mental activity through the day, continue on with what’s working for you.

Intermittent Fasting Boosts Metabolism

A recent review of studies showed promising metabolic effects of IF and another study suggests that intermittent fasting appears to be preventative in terms of keeping metabolism from slowing. Short-term fasting actually increases metabolism, due to an increase in catecholamines (stress hormones). It’s long-term, chronic calorie restriction that causes a metabolic slowdown, not any particular meal pattern over the course of the day.

Overall, intermittent fasting appears to be one more tool in the toolbox for people who would like to lose weight, but it’s not for everyone.

Certain Foods Increase Your Metabolism.

This one causes so many people to burn their mouths off at dinner time but it is more myth than truth. Your body does see an increase in thermogenesis (the production of heat) when you eat certain foods such as hot peppers, caffeine, apple cider vinegar and some others. An increase in thermogenesis will technically cause you to burn more calories – but this effect is short lived (30minutes or less) and has little to no effect on metabolic rate or weight loss.

Eating Before Bed Causes Fat Gain

While your metabolism slows a bit through the night, it never stops. When you eat has little impact on this process. Eating food before bed, depending on your choices, can impact sleep which in turn will impact your metabolism. Overeating at night, or choosing nutrient poor options will cause fat and weight gain. If you are hungry before bed, have a small, nutritious snack, and don’t stress about it.

Fidgeting Boosts Metabolism.

NEAT actually accounts for the majority of your non-resting energy needs. People who move more in general tend to be leaner, as are people who fidget. Fidgeting all the time can be really distracting, so you might simply want to focus on moving more. This means more standing, walking instead of driving to do your errands, and doing your own gardening.

Low Calorie Diets Slow Metabolism

Your body is VERY smart and is programmed to hold on to fat. Evolutionarily, this was an adaptation to survive through times of feast and famine. When you severely restrict your energy supply over the long term, your body will make fat loss difficult for you.

When you manage to lose fat through caloric restriction, your body adapts in several ways:

  • Hormones slow your metabolic rates to conserve energy along with increasing hunger in order to drive you to eat more.
  • Caloric restriction also results in muscle loss, slowing metabolic rate even further. When you lose weight, you become physically smaller, and therefore your body requires less energy.
  • Long term caloric restriction will eventually mean you require less and less energy until an unsustainable diet calorie level is reached.

If you want to lose weight without downshifting your metabolism while you do it, focus on building muscle mass through exercise, and avoid reducing calories too much. Concentrate eating with Paleo principles in mind - more whole or minimally processed foods, less processed, manufactured junk.

There are no shortcuts to health. At the end of the day, the easiest thing you can do to keep your metabolism working as efficiently as possible is to treat your body well by supplying it with adequate nutrients, lots of movement exercise, sufficient sleep and avoiding unnecessary stressors. A happy body is a healthy body and a Paleo lifestyle paves the way!

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