Thermogenesis is a term that refers to any process that generates heat. Diet-induced thermogenesis looks at the potential impact of our food choices, the body's regular digestive processes, and the energy required to break down that food on the body's heat production. Because this process inherently burns calories, it's often suggested that diet-induced thermogenesis should be considered part of any plan to change body composition or lose body fat. It may be used to guide nutritional recommendations to support those goals.
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What is Diet Induced Thermogenesis?
Diet-induced thermogenesis increases how much energy you expend beyond your basal metabolic rate (BMR). It is calculated by dividing that increase by the energy content of all the food you eat. As such, diet-induced thermogenesis is typically expressed as a percentage. Along with basal metabolic rate (BMR) and activity-induced thermogenesis (how many calories you burn from activity), it's one of the three main components that goes into daily energy expenditure, or how many calories you "burn" each day.
On average, diet-induced thermogenesis can contribute anywhere from 5-15% of total daily energy expenditure, depending on the content of the diet.
Do Foods Really Boost Metabolism?
While it's common to see articles claiming that certain foods will "boost metabolism," it's important to understand what impact foods are actually having on the metabolism. Some foods can increase the rate of thermogenesis after they are consumed, though these effects are typically short-lived and do not impact the basal metabolic rate over time.
Capsaicin, green tea, and protein-rich foods like meat, poultry, fish, and eggs all have been linked to a higher impact on diet-induced thermogenesis, requiring more calories to digest and break down. Protein has roughly a 30% thermogenic effect, meaning that for 100 calories of protein consumed, 30 of them are used to digest the protein, with the 70 remaining available to be used as energy for basic metabolic functions.
Ultimately, the main determinants of diet-induced thermogenesis are how many calories are consumed in one's diet and the percentage of protein that makes up those calories.
Protein Thermogenesis
Protein sources, in particular, play an important role in diet-induced thermogenesis and body weight regulation, as protein improves satiety and results in a higher rate of diet-induced thermogenesis.
Protein tends to stimulate diet-induced thermogenesis to a greater extent than either carbohydrates or fat. For this reason, a higher-protein diet is often recommended for those looking to lose body fat and change their body composition - higher-protein diets not only increase the number of calories you're expending just due to digesting the macronutrient, but high protein intake is also linked to better satiety, meaning those eating higher-protein diets tend to consume fewer calories overall.
Studies suggest that diet-induced thermogenesis increases the most with at least 30 grams of protein in a meal, with animal protein sources having a slightly higher rate of thermogenesis (2-3% more than plant-based sources).
Impact of Brown Adipose Tissue on Diet-Induced Thermogenesis
Brown adipose tissue is a kind of body fat activated in response to cold exposure. Its primary role is producing heat to help the body maintain the proper temperature, which requires calories. Research has found that brown adipose tissue may also play a role in diet-induced thermogenesis. Production of gut-related hormones and compounds such as bile acids not only contributes to diet-induced thermogenesis but also activates brown adipose tissue directly, helping to increase thermogenesis overall. Additionally, the thyroid gland plays a role in this connection, with adequate thyroid function needed for activating brown adipose tissue and optimal thermogenesis.
Since morning cold plunges have become popular additions to a lifestyle that supports overall metabolic health, it could be that the activation of brown adipose tissue plays a role in the purported body composition benefits of cold plunging. Pair that with the fact that diet-induced thermogenesis has been found in studies to be higher in the morning than the evening, and it may lend credibility to why those who eat earlier in the day and participate in biohacking modalities like a morning cold plunge see favorable body composition changes - it may be due to an amplified diet-induced thermogenic response.
Functional Medicine Labs to Test for Patients Wanting to Lose Body Fat Percentage
The following functional medicine labs can be utilized to assess areas that contribute to diet-induced thermogenesis:
Comprehensive Stool Test
Since adequate digestion and absorption are central to diet-induced thermogenesis, it can be helpful to evaluate the health and function of the GI (digestive) system through a comprehensive digestive stool analysis. A healthy gut produces all of the necessary enzymes and compounds needed to digest food, activate brown adipose tissue, and increase metabolic rate in response to the diet; without adequate production of, for example, bile acids, the diet-induced thermogenic response described above may not be as optimal.
Thyroid Panel
Since thyroid function helps modulate thermogenesis as a whole, in addition to the activation of brown adipose tissue, it can be helpful to assess if one's thyroid is working optimally. There's also a close link between thyroid function and bile acids, meaning a full thyroid panel can help provide insight into the bigger picture of how well the metabolic pathways underlying diet-induced thermogenesis are functioning.
Body Composition Scan
Understanding your body fat percentage and the amount of muscle mass you have can be helpful when considering your total daily energy expenditure, calculating the amount of protein and other macronutrients in your diet, and ensuring any weight loss efforts are producing loss of body fat rather than valuable muscle mass.
What Are The Top Foods That Improve Thermogenesis?
The ideal nutritional approach to improve thermogenesis would be a diet that meets protein needs or protein-forward nutrition. While many "diets" fit the bill, the diet likely to lead to the highest rate of diet-induced thermogenesis would be a higher protein diet.
Adding in foods such as capsaicin (cayenne pepper) and green tea may also be helpful, and choosing primarily whole food sources of fats and carbohydrates (versus processed foods) would be ideal.
Supplements and Herbs That Improve Thermogenesis
Many supplements are labeled "thermogenic aids" or "fat burners," with a few ingredients in common that may improve thermogenesis. However, it's critical to note that many of these supplements marketed as "fat burners" contain amounts far beyond a "single" serving of a given compound and are not well-regulated regarding safety and efficacy. Below are several supplements supported by literature regarding their impact on thermogenesis.
Green Tea Extract/ECGC
Green tea extract and its catechin content have been linked to increases in energy expenditure and thermogenesis, as well as increased fat oxidation. While some studies suggest that any thermogenic aid has a risk of increased heart rate and blood pressure, green tea extract is one of the safest aids, with a daily intake of 338mg or less in a supplemental form deemed safe.
Caffeine
Caffeine intake has been linked to increased thermogenesis and brown adipose tissue activation. However, many "thermogenic aid" supplements have high amounts of caffeine, up to four times the amount you'd get from drinking one cup of coffee. Higher caffeine intake also increases the risk of short-term elevated heart rates, palpitations, blood pressure, and anxiety. For those with higher cardiovascular risk, caffeine may not be the best thermogenic aid to consider.
Cayenne pepper (Capsaicin)
Capsaicin supplements have been linked to weight loss through the effect of capsaicin on thermogenesis. However, the impact may be seen more in lean individuals, as studies have shown inconsistent results in obese populations. Up to 6mg taken daily for 12 weeks has been shown to have favorable effects on body composition, especially when paired with a healthy diet and exercise plan.
Other Strategies for Increasing Diet-Induced Thermogenesis
In addition to diet composition, studies also show that eating slowly and ensuring that you're chewing your food thoroughly helps to increase the rate of diet-induced thermogenesis. So if you're working on a body composition goal, make sure you're taking the time to pause, slow down, and intentionally chew your meal. This helps with the digestive process and production of enzymes and hormones important for digestion and translates to expending more calories while digesting your food.
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Summary
Diet-induced thermogenesis refers to the impact your food and digestion can have on the calories expended each day. The amount of brown adipose tissue (BAT) one has can correlate with more efficient diet-induced thermogenesis, and diets higher in protein tend to impart a higher percentage of diet-induced thermogenesis to total daily energy expenditure, making them ideal for those looking to lose body fat percentage. Last, diet-induced thermogenesis is more efficient earlier in the day than at night, which is an important consideration for meal timing and planning as part of a larger holistic approach to one's nutrition.
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