Tag: Energy Expenditure

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Boosting Metabolism – Myths & Facts

Metabolism Boost

Beware the allure of products and diet systems offering faster fat burning results and “metabolism boosting” effects – there is no silver bullet.

Your metabolism isn’t broken and your near-term fat loss goals are achievable provided they are part of a longer-term strategy. Utilize time-tested practices to keep your metabolism humming that don’t require supplements or elimination of foods.

How metabolism slows during weight loss

Decrease in resting metabolic rate (RMR)

Your body expends energy to keep you alive and at your current body weight. The more you weigh, the more energy required to keep you alive.

During weight loss, you become a smaller human being. It’s logical that you will burn fewer calories to survive as a smaller human. Alterations in autonomic nervous system and neuroendocrine function (notably, downregulation of thyroid hormone) decrease energy expenditure by decreasing heart rate, blood pressure, and muscle ATP consumption.

Decrease in non-exercise activity

There may also be reductions in energy expenditure greater than what can be predicted from predicted by a loss of body mass. This is known as adaptive thermogenesis.

A main component of adaptive thermogenesis is decreased non-exercise activity. It could be less fidgeting and moving about, more time sitting, or walking a little less. This decreased activity is often imperceptible, but equates to fewer calories burned per day. On top of this total lower amount of movement, less energy is required during that movement because your body is lighter.

Further, feelings of hunger and reduction in satiety play into the issue with upregulation of appetite stimulating hormone (ghrelin) and downregulation of appetite suppressing hormone (leptin) during calorie restriction. The simultaneous decrease in RMR and general activity, combined with increased hunger and reduced satiation create an environment to regain weight, perhaps even exceeding previous highs.

The best way to “boost” metabolism is to increase calories to maintenance levels*

Slowing of metabolism due to adaptive thermogenesis is small if you’re following a reasonable diet strategy, and can be all but eliminated through periods at maintenance calories. This can be accomplished by:

  1. Diet Breaks. usually, 1-3 weeks at maintenance calories during a dieting phase). These diet breaks do appear to be psychologically beneficial, provide metabolic support through suppression of appetite, and may also help with motivation in the gym!
  2. Maintenance Phases. Weeks to months at maintenance calories after a set period of dieting.

Energy expenditure will increase with increased energy and support recovery from the physical and mental fatigue associated with dieting. It may also help with training motivation and getting more out of your workouts.

If energy restriction has been severe, or you have been chronically dieting it may require an extended period at maintenance calories. Giving yourself the grace of time, and focusing on a balanced and micronutrient-dense diet is critical. Increasing calories to maintenance levels should not mean a big change in the foods you’re eating, it just means a little bit more food, and a little bit more flexibility. Meeting your protein requirements and consuming veggies and fruits per day should continue to be the foundation.

*This is not to be confused with the clickbait phrase “eat more to lose weight”, which is in reference to transitioning from highly processed, high calorie density foods to lesser processed, less calorie dense foods resulting in reduce calorie intake for more food volume. What I’m referring to above is intentionally increasing calories (taking yourself out of energy deficit in a controlled way) for a period of time, so that your body in a good position to make the best progress during a subsequent diet phase.

Ignore marketing hype.

There’s no evidence pointing to a boosted metabolism using certain diet type. Outcomes for fat loss are similar comparing keto, low carb, and intermittent fasting to lower fat, higher carb diets (at the same calorie and protein levels). Terms heavily relied upon by ketogenic and low carb diet marketers are turning your body into a “fat burning machine” or “reprogramming” the body to use fat for fuel. Fat burning (oxidation of fatty acids for energy) is NOT the same thing as losing body fat.

Net energy dictates gain (calories in > calories out), maintenance (calories in ~ calories out), or loss of tissue (calories in < calories out)

  • If you eat more calories from fat, you will burn more fat AND store more fat. If your diets is low in carbohydrates, your body will become more efficient at oxidizing fatty acids for energy (aka fat adaptation). This does NOT mean you will lose body fat! Net energy deficit dictates loss of fat.
  • If you eat more carbs, you will expend more energy from carbs, store carbs in your muscles, and convert excess to fat. If your diet is higher carbohydrate, your body is more efficient at oxidizing carbohydrates for fuel.

Take home points

  • Avoid extreme calorie restriction.
  • Take fat loss in discrete phases, versus chronic dieting
  • Form habits around maintaining daily activity (not related to exercise). For example, a 5-10 minute walk on a work break or in the evening after dinner. Identify pleasurable activities that you can stick with long after the dieting period is over.
  • Hit your protein target within your calories because it 1) supports your lean mass and 2) has a slightly higher energy cost to absorb and digest, for a marginal addition to daily energy expenditure.
  • Eat foods that satisfy you and make you feel great. The best healthy nutrition habits are the ones you can stick with.

I hope you found this helpful. Have any questions? Please contact me.

Follow me on IG @kmcgrath.phd and Facebook for more insights.

Further reading:

Hall, K.D. Metabolic Adaptations to Weight Loss. Obesity 26, 5 (2018).

Nunes, C.L.; Casanova, N. et al., Does adaptive thermogenesis occur after weight loss in adults? A systematic review. Br J Nutr., 25, 1 (2021).

Garthe, I.; Raastad, T.; et al., Effect of two different weight-loss rates on body composition and strength and power-related performance in elite athletes. Int J Sport Nutr Exerc Metab., 21, 97 (2011).

Trexler, E.T., Smith-Ryan, A.E. & Norton, L.E., Metabolic adaptation to weight loss: implications for the athlete. J Int Soc Sports Nutr 11, 7 (2014).

Drummen, M.; Tischmann, L.; et al., High Compared with Moderate Protein Intake Reduces Adaptive Thermogenesis and Induces a Negative Energy Balance during Long-term Weight-Loss Maintenance in Participants with Prediabetes in the Postobese State: A PREVIEW Study. J Nutr., 150(3), 458 (2020).

Rosenbaum, M.; Leibel, R.L. Adaptive thermogenesis in humans. Int J Obes (Lond), 34 Suppl 1, S47 (2010).

Peos, J.J.;, Helms, E.R., et al., Continuous versus Intermittent Dieting for Fat Loss and Fat-Free Mass Retention in Resistance-trained Adults: The ICECAP Trial. Med Sci Sports Exerc. 53(8), 1685 (2021).

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Understanding Daily Calorie Burn

A breakdown of how your body expends energy. How can we manage calorie burn to our advantage?

On our pursuit to achieve health and fitness goals – whether it be to lose fat, increase muscle, or maintain healthy weight, control of daily calories consumed (energy intake) is critical to the process. We manage this by the quantity, type, and quality of foods we eat. Energy expenditure, or daily calories burned (total daily energy expenditure aka TDEE) is equally as important. We do have some degree of control over calorie burn, so let’s take a closer look at the four key contributing elements of TDEE and understand what we should focus on to gain the most advantage.

Basal metabolic Rate (BMR)* contributes ~70% to total daily energy burn. It represents the number of calories the body consumes at rest to perform essential functions such as breathing, circulation of blood, brain function, temperature regulation, and cell turnover. You burn this energy 24h/day, whether awake or asleep.

Day to day, you cannot influence BMR. The primary factors dictating BMR are height, weight, age, and gender. Smaller people have a lower BMR than larger people. Body composition and hormones also exert influence; leaner individuals have a higher BMR.

Over longer periods of time, BMR can change. As we lose weight our BMR decreases and as we gain weight our BMR increases. However, in the grand scheme we should not look to BMR as a significant factor to manipulate total daily energy expenditure.

Nonexercise Activity Thermogenesis (NEAT) contributes ~15% to total daily energy burn. It represents the number of calories your body consumes through general movement (excluding intentional exercise). Examples include fidgeting, walking around throughout the day, taking the stairs, and running errands.

Daily activity level has an enormous impact on the calories you burn. Studies on people who have sedentary office jobs versus people who have physically strenuous jobs have indicated a 2-3X difference in NEAT – upwards of a 1000 kcal difference per day! It is the main reason why it seems some people can eat more without gaining weight.

Focus on NEAT if you are seeking to lose weight. During a fat loss diet, the most effective and proven way to create a calorie deficit is through reduction in food intake combined with additional movement. Additional calories burned by simply walking around more can be a game changer to maintaining an appropriate calorie deficit. It’s absolutely an element to evaluate if weight loss has stalled – as we continue long enough in a calorie deficit, we are inherently inclined to move around less. NEAT is decreasing as we move through the diet phase and we probably hadn’t even realized it.  Given that is it so important, I’ll have a separate post on NEAT soon.

Buddy’s Spaghetti and M&M’s dinner are probably not the best choice……

The thermic effect of food (TEF) contributes ~10% to overall daily calorie burn. It represents the energy used (beyond BMR) to extract and process nutrients from the foods we eat – digestion, absorption, and excretion. At face value it doesn’t appear to be something that we have much influence over. However, we do have some degree of control over TEF through food selection. 10% is a general estimation and will be higher or lower depending on the relative amount of protein, carbohydrates, and fat you consume, as well a person’s fat free mass (leaner individuals generally have a higher TEF).

  • Protein is the most energetically costly macronutrient for our bodies to process – 20 to 35%. For example, if I were to eat 350 kcal worth of protein, I need somewhere between require around 70-120 kcal to digest it.
  • Carbohydrates require 5-15% of their energy to process. Fiber-rich carbohydrates will be on the higher energy burn end of the spectrum – think vegetables, fruits, rice, and whole grains – versus simple or highly processed sources.
  • Fats require a minimal amount of energy to process – 0 to 5%. This doesn’t mean that we should avoid them to keep our TEF higher; fats serve and important role in the diet. Rather, we should focus more on unsaturated sources that can provide the most health benefits, e.g. olive oil, nuts, seeds, and omega-3 rich sources found in many types of fish.

Note: TEF is an area where the basic “calories in – calories out” equation is an oversimplification. Because we all use different amounts of energy to process the foods we eat, we cannot simply say that 100 calories worth of peanut butter is equal to 100 calories worth of chicken – once ingested they have different energy costs in our bodies so net calories will be different despite having an equivalent 100 calorie absolute energy value pre-ingestion.

Exercise Activity Thermogenesis (EAT) contributes ~5% to total daily energy burn. Although EAT usually contributes a lower percentage of your total calorie burn compared to NEAT, it is strongly influenced by exercise modality, duration, intensity, body size, and genetics. Try to get an hour of exercise 3 – 4 days a week. The health benefits extend far beyond basic weight management.

Bottom Line

As it relates to total daily calorie burn and fat loss, focus on what you can exert the most control over!

NEAT: Increase your general activity level during the day – if you have a sedentary job, dedicate specific times of day that you will stand up and walk around.

TEF: Your diet should contain adequate protein (0.8 -1 g/lb. of bodyweight) and contain carbohydrates sources that are high in fiber and minimally processed.  Fats should remain in your diet from healthy sources.

EAT: Get some form of dedicated exercise 3-4 x week. Ideally, incorporate resistance training in your routine to support lean mass retention and fat loss/muscle gain, which will drive further increases across all key elements of total daily energy expenditure.

*You may also come across the acronym RMR, or Resting Metabolic Rate. BMR and RMR are slightly different, but for the purpose of this post they can be used interchangeably.

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