Author: Paul Hollinrake, Researcher & Trainer in Public Health/7 June 2018
In a previous blog, limitations of the energy balance theory were discussed. If you don’t have the time to read this at the moment it can be summarised as:
A calorie is defined as a unit which is used to measure energy. The calorie seen when one is referring to food is actually a kilocalorie (1,000 calories). A calorie (kcal) is the amount of energy required to raise the temperature of 1kg of water by 1o It is also worth considering sometimes kcals are expressed as kilojoules (kJ) where one kcal equates to 4.184kj.
The eat less (calories in) and move more (calories out/expended) mantra is too simplified
Calories in and out are not independent but are related, e.g. when calories are reduced, metabolism (BMR) can also reduce
Hormones can drive hunger, satiety and fat storage
Not all calories are equal e.g. 100kcals of extra virgin olive oil is not the same as 100kcals of pure fructose.
Counting calories using technology such as Apps, smart watches and websites seems to be popular at the moment, Google A.I. is even learning how to predict calories from photos. Despite these devices having their own inaccuracies, this blog will discuss some of the limitations of counting calories in addition to the points raised above.
Counting calories, where it all began
In 1848, a chemist from Ireland, Thomas Andrews discovered that setting food on fire in a chamber and measuring the temperature change in water that surrounded the chamber (named a bomb calorimeter), he could estimate the calorie content of food. However, humans are not bomb calorimeters. And in 1896 Wilbur Atwater an American scientist from the Department of Agriculture investigated the calories in more than 4,000 foods which were collected at the world’s food fair. He did this by feeding the foods to his subjects and then collected the faeces which were analysed in a bomb calorimeter.
This led to the Atwater calorie values, which are numbers that reflect the available energy in each gram of carbohydrate, protein, and fat. However, he did find that even in the same types of foods (i.e. apples) that were grown, picked and stored the same way, there was a wide range of values found. The average numbers of 4 kcals per gram of protein, 9 kcals per gram of fat and 4 kcals per gram of protein are supposed to reflect how much energy we absorb from food and are known as Atwater general correction factors. But it gets more complicated than this, we have to consider so much more.
What we need to know
Since Atwater’s work, it has been discovered that carbohydrates high in fibre can have different correction factors which can depend on the type of fibre and a person’s gut bacteria. In addition, protein absorption can vary, with animal protein providing more energy than vegetables e.g. 4.36 kcals from eggs, 2.44 kcals from most vegetables.
How you prepare and eat your food can also impact the calorie count. Chopping, blending and cooking food increases the calorie count because it begins the process of digestion which is a natural function in human digestion, and has an energy cost. For example, a jacket potato can almost double in calories when cooked, 101 to 193 kcal with an egg changing from 47 to 74 kcals. This is not accounted for on a food label.
Even if calorie values were correct, we are not good at portion control. Studies have shown that we can get portion sizes wrong at least two-thirds of the time, and this can include trained nutritionists who can underestimate the calories in meals by 30%. For example, this could mean a heaped tablespoon of peanut butter could be nearly 100 kcals more than a level tablespoon, very easy to do. So is there a better option?
Researchers are investigating the possibility of personalised nutrition for health, this can involve the influence of DNA (nutrigenomics), eating foods that promote your individual gut bacteria (probiotics) and metabolomes (thousand’s/millions of chemicals that help to metabolise food). However, although these sound promising, it is still early days and nothing conclusive can be recommended at the moment.
The bottom line
Counting calories introduce a large margin of error, one that is estimated to be on average around 25%. So if you think you are consuming 2000 kcal, this figure could actually be in a range of 1500 – 2500 kcals. So perhaps not that helpful or worth the effort after all.
Instead of counting calories, eat a wide range of nutrient-dense food and eat to appetite and true fullness (not because of stress or boredom). Tuning into the quality of your diet by eating fresh, non-processed food, monitoring how you feel and tracking body changes (e.g. weight, waist circumference) will be the best approach for now.
As with all our blogs and other work we would love to hear your thoughts and feedback, so please feel free to drop me an e-mail at firstname.lastname@example.org or message us on Facebook, tweet us at @XPERTHealth or follow us on Instagram @XPERThealth.
Further reading and key references
Atwater, W.O. & Woods, C.S., (1896). The Chemical Composition of American Food Materials. Bulletin 28. USDA. Washington, D.C.: Government Printing Office.
Carels RA, Harper J, Konrad K. (2006). Qualitative perceptions and caloric estimations of healthy and unhealthy foods by behavioural weight loss participants. Appetite. Mar;46(2):199-206.
Carels RA, Konrad K, Harper J. (2007). Individual differences in food perceptions and calorie estimation: an examination of dieting status, weight, and gender. Appetite. Sep;49(2):450-8.
Carmody RN, Wrangham RW. (2009). The energetic significance of cooking. J Hum Evol. Oct;57(4):379-91.
Carmody RN, Weintraub GS, Wrangham RW. (2011). Energetic consequences of thermal and nonthermal food processing. Proc Natl Acad Sci U S A. Nov 29;108(48):19199-203.
Greenfield, H., 2003 (updated 2014). Food composition data: Production, management and use. Burlingame, B.A. & Charrondiere, U.R. (Eds.), Rome, Italy.: Food and Agriculture Organization of the United Nations.
Groopman EE, Carmody RN, Wrangham RW. (2015). Cooking increases net energy gain from a lipid-rich food. American journal of physical anthropology;156(1):11-18.
Lansky D, Brownell KD. (1982). Estimates of food quantity and calories: errors in self-report among obese patients. Am J Clin Nutr. Apr;35(4):727-32.
Savov, V (2014) Calorie counting leads to bad science and worse gadgets, https://www.theverge.com/2014/6/3/5763960/calorie-counting-leads-to-bad-science-and-worse-gadgets
Wishart, D (2018) Metabolomics, https://www.metabolomicscentre.ca/science