7.1 Calorie restriction or exercise for weight loss?
The figures in section 3.5 may not make it completely obvious but they do show that trying to achieve weight loss by exercise alone would require a great deal of effort. To achieve the 0.7kg weekly weight loss I obtained by cutting 5369 kcals per week from my food intake would take about 4.75 hours a week running at 6km/hr on a treadmill inclined at 18%, which is a level of exercise that definitely counts as vigorous! To lose 1kg a week on the same treadmill would require almost 1 hour of vigorous exercise every day. That level of commitment and effort is probably going to be impractical for most people with a busy job. However, while trying to achieve all the weight loss via cardio alone is probably not the optimum approach for most people, it is certainly a good idea to combine a calorie restricted diet with regular cardio and resistance training sessions. Not only is regular cardio a key indicator of future health but the boost to metabolic rate seems to last for a lot longer than the actual training session to help the fat disappear. Resistance or weight training does not burn that many calories per session compared to cardio but I find that its effects last even longer – I always feel hungrier on the day after a weights session than a cardio session and this probably reflects that the body has to do more recovery work after a weights session to repair the muscle fibres and add lean muscle mass. All that adds up to more calories being consumed long after the exercise has finished.
If you perform cardio exercise in the gym then most machines directly provide an estimate of the calories burned. Weightlifting will not burn many calories directly, only about 112 kcals for a “moderate” level, but I find the recovery effect continues to burn calories into the next day. If you want to work out how many calories you burn on other significant one-off events like hill walking, cycling, or even running up stairs then here are useful online calculators which can provide an estimate of the kcals consumed :
7.2 Recommended levels of regular weekly exercise
The NHS provides guidelines on how much exercise we should do each week to gain significant health benefits. It recommends we do both aerobic exercise and strength exercises :
Adults aged 19-64 should do 150 minutes each week of moderate aerobic activity and strength exercises on at least two days per week that work most of the major muscles (legs, hips, abdomen, chest, shoulders, and arms. Alternatively you can perform 75 minutes of vigorous exercise each week along with the strength exercises.
But what constitutes “moderate” and “vigorous” levels of exercise intensity? To answer that question we need to introduce the MET unit where MET stands for Metabolic Equivalent. The MET is defined as a measure of exercise intensity based on oxygen consumption. More specifically, a single MET is defined as the amount of oxygen a person consumes (or the energy expended) per unit of body weight during 1 minute of rest. It is equal to about 3.5ml of oxygen consumption per kilogram (kg) of body weight per minute, or 1kcal per kg of body weight per hour. The key point is that 1MET represents the minimum energy we need to support our metabolic functions when we are completely at rest so expressing exercise levels in METs provides a measure that is specific to your individual body weight.
1 MET is defined as 1kcal/hour per kg of body weight. I weigh 68kg so 1MET for me is easily calculated as 68 x 1kcal per hour = 68kcals per hour. In a full 24 hours that means that my basic metabolic functions will consume 68 x 24 = 1632 kcals. So, if we assume the average 2400kcals per day energy requirement, then we can see that the basic functions needed just to stay alive consume approximately 70% of my daily energy intake. Of course we use more energy when we are active in daily life or exercising and we can use the MET to define any level of exercise relative to the basic energy needed to stay alive at complete rest.
So how do you relate the NHS guidance on exercise to what you as an individual need to do? 1 MET for you is your weight in kg expressed as kcals/hour. So if you weigh 50kg then 1 MET = 50 kcals/hour. Once you know what 1MET represents for you in kcals/hour you can then work out the intensity of moderate and vigorous exercise using the definition that follow.
Light exercise is defined as less than 3 METs
For example : walking slowly (i.e. shopping, walking around the office), sitting at your computer, making the bed, eating, preparing food, and washing dishes. For someone weighing 68kg like me, that means exercising at up to 204 kcals/hour.
Moderate exercise is defined as 3 to 6 METs (i.e. between 204 and 408kcals/hour for anyone weighing 68kg, like me)
For example : sweeping the floor, walking briskly, slow dancing, vacuuming, washing windows, shooting a basketball. Moderate exercise by the NHS definition would therefore require at least 22 minutes every day exercising at an intensity of between 204 and 408 kcals/hour.
Vigorous exercise is defined as more than 6 METs (i.e. greater than 408kcals/hour for anyone weighing 68kg, like me). For example : running (5 mph >), swimming, shovelling, football, jumping rope, carrying heavy loads (i.e. bricks). Vigorous exercise by the NHS definition would therefore require at least 11 minutes every day exercising at more than 408 kcals/hour.
If you do cardio exercise on a treadmill, cross trainer, or rowing machine then the calories expended can be read directly from the display. For non-gym activities the “Compendium of Physical Activities” provides an extensive list of activities with their estimated METs : https://sites.google.com/site/compendiumofphysicalactivities/ The point is that you do not have to be in a gym to exercise. All forms of exercise count, just aim for the recommended 150 minutes of moderate exercise per week.
If you use the TDEE calculator referred to earlier in section 3.4 it will provide an estimate of your individual energy requirements based on several scenarios such as “sedentary”, “light exercise”, etc. Entering my characteristics (Age 64; Male; Height 174cm; Weight 68kg; Body fat 8.3%) it calculates the following estimates for my energy needs :
Basal Metabolic Rate : 1721kcals
Sedentary : 2066kcals
Light exercise : 2367 kcals
Moderate exercise : 2668 Kcals
Heavy exercise : 2969 kcals
Athlete : 3270 kcals
Note that it calculates a slightly higher BMR than the 1632 kcals I calculated above using the 1 kcal/kg of body weight conversion factor, probably because the TDEE calculator has more variables to work with, such as body fat, than the simple generic formula of Weight x 1kcal/hour.
7.3 Reversing risk of heart disease caused by a sedentary lifestyle
I have often heard people say that it is too late in life for them to start exercising as they have never really exercised before. I would dispute that view as I know from experience that the body will start to react immediately to any exercise. In fact a recent clinical trial of adults aged 45-64 has shown that the risk heart disease can actually be reversed even if you start late in middle age after years of a sedentary lifestyle : http://www.bbc.co.uk/news/health-42565137 Beyond the age of 65 the benefits begin taper off as the elasticity of the heart wall reduces, so do not wait too long if you want to reverse years of inactivity!
7.4 Muscles do burn energy at rest, just not very much!
One of the somewhat specious arguments in favour of weight training is that muscles burn more energy at rest than fat does and that if you add more muscle you can be losing weight while you sit. It sounds wonderful but, although the basic premise is true, the claims made appear to be significantly exaggerated. So if you think that adding a bit of muscle will help you significantly with fat loss you are probably going to be disappointed.
There is a huge amount of contradictory information on the web on this topic. Some sources claim that muscle burns fifty times more energy at rest than fat, but the latest thinking appears to be that the figure is probably closer to a factor of three, which is still better than nothing of course.
How many calories do muscles burn at rest? I have seen figures for a pound of muscle range from 50 calories per day to 6 calories per hour (which would be 144 calories per day) but I could not find any substantive clinical studies to back up these numbers. This article : http://articles.latimes.com/2011/may/16/health/la-he-fitness-muscle-myth-20110516 tends to debunk the wilder claims that have been made and suggests that a 200 pound man who gained 20% of his body weight as muscle (which would involve very significant effort over many years) might only increase his resting metabolic rate by about 120 calories per day. This is very much less than the “50 calories per day per pound of muscle” theory which would predict an increase of 1000 calories per day in resting metabolic rate. The reason for this is that muscle mass is responsible for only about 20% of the body’s Resting Metabolic Rate so increasing muscle mass by 20% will only increase the metabolic rate by 20%x20% = 4%.
To put this in context : I am 64 years old, 1.74m tall, and weigh 68kg so my Resting Metabolic Rate = 1457 calories per day. You can calculate your own RMR here : https://www.bodybuilding.com/fun/calrmr.htm So even if I added 20% of my body weight as muscle (which is probably totally unrealistic for a 64 year old male) my Resting Metabolic Rate would change by only 20%x1457 = 58 calories per day.
So adding more muscle in an attempt to burn fat while you are sitting down should not be your primary fat loss strategy! Weight training should be seen as complementary to cardio exercise and the combination definitely does provide significant health benefits (such as reducing the risks of osteoporosis and diabetes). Just don’t expect it to help significantly with actually burning fat while sitting or even during the actual weight lifting sessions where lifting moderate weights might consume only about 225 calories per hour. Nonetheless I find that the effect of an hour of weightlifting, in spite of the fact that it might only require 225 calories seems to have a much greater effect on my need for food than 90 minutes on the treadmill where I might burn 1350 calories. I always feel much hungrier after weight training than with cardio and that feeling usually lasts well into the next day.
While I do not understand fully the reasoning behind this difference it appears that the explosive energy usage in weight training means that the exercise is “anaerobic” where the body tends to get most of the energy it needs directly from carbohydrates. Cardio exercise, in contrast, is considered “aerobic” and in this mode the body obtains energy from both carbohydrates and stored fat, hence why some treadmills have an indicated “fat burn” intensity zone.
There is a lot more on-line on this subject but the bottom line is that if you want to lose weight fast then focus on vigorous cardio, but if you want the optimum in weight loss, fitness and health then add in some weight training as well. I split my time in the gym roughly 70% cardio and 30% weights.
7.5 Fast Exercise
In his documentary “Eat, fast, and live longer” Mosley looked at the effects of exercise and, in particular, the role of High Intensity Training (HIT) in complementing the health benefits of fasting on our body cells. HIT involves as little as 3x20 second bursts of intense exercise repeated three times a week and, although it seems too good to be true, this pattern of exercise can increase your aerobic capacity by the same amount as hours of less intense exercise in the gym and help keep you blood lipids under control. A small proportion of the population, because of genetic makeup, will not respond to HIT in this way but for most people it is a good way to stay fit if you do not have the time or inclination to pound away for hours in the gym every week.
In his book “Fast Exercise” Mosley delves deeper into the effects of exercise on our health and fat burning capability. He explains how to start HIT as well as a regime of other exercises that can be incorporated in to your 5:2 Fast Diet programme which do not involve sweating for hours in the gym. This is about exercising smarter not harder.