No, not part 3 of the weight loss series, don't worry. Rather, it's a response to your many emails and comments to Part 2 of the series that looked at calories in, calories out, and the principle of weight loss. As usual, there are too many good comments to do justice to with an answer, so I'll thank you once again and move ahead to a general response. Also, I wanted to write briefly on what is still coming, because there are some things I want to cover in future posts which come up over and over in the early posts as well.
One common theme in your responses has been 'complexity', and this is something that has weighed (pardon the pun!) on me as I've written these last two posts. As I stressed yesterday, weight loss is not simple (obesity wouldn't be the fastest growing cause of death if it were), but at the same time, it must be simplified, because so many layers of misinformation have been added over the years (and the 87,000 books) that many have become entrenched as 'best practice' that it actually serves to go back before going forward!
The simplicity is the calories argument, the principle that energy out must exceed energy in for weight loss to occur. However, I wouldn't recommend taking the approach of counting calories to try to balance the equation, because of inaccuracy and unknowns on both sides of the 'scale'. I explained this a little yesterday, but there were two points that I didn't stress enough, and I have some of you to thank for raising them.
First, let's look hypothetically at someone whose energy intake is 3000 kCal per day, and who exercises regularly and is in weight balance. This person could, in theory, get that energy from 333 grams of fat. They could also get it from 750 g of starches. Neither is desirable, for both the obvious reason that a diet consiting entirely of only one food group would be sorely lacking in important nutrients and you'd end up less healthy than Morgan Spurlock (the guy from Supersize Me).
However, what is more vital is to recognize that you don't simply add up the numbers, because the macronutrients (carbs, fats and proteins) have a more complex role than simply adding calories to the body. Carbohydrates are the primary source of energy during exercise, and for the brain pretty much all the time. Fats play a role in cell function, and proteins are crucial for cell repair and for muscle recovery after exercise. You can have too little of each, particularly carbohydrates. Perhaps the biggest trend in fad diets in recent years is the shift away from carbohydrates, with the principle that fat can provide energy. That's true, but only up to a point, and an athlete without carbohydrates is a dangerous proposition - impaired performance and immune function are two of the consequences.
The point is that your objective with diet is not to simply tally up the calories, you also have to manage the diet for health reasons. There are many theories on how to achieve this - there's a 40-30-30 principle, which says that 40% of your energy should come from carbs, and 30% each from fats and proteins. Then there's the theory that those doing more exercise should aim for 60-30-10, then there are the "anti-carb" diets where only 10% of the energy comes from carbohydrates, with most from proteins. There is a great deal of debate around these diets, which balance is optimal. I'll try to get to that later in the series, or in a separate post in collaboration with a dietician (because if you want to offend people, tell them their diet is not optimal). I firmly believe, however, that anyone who is basing their weight loss on exercise, or who is training for performance, must ensure that their carbohydrate intake is sufficient, or they will be compromised.
Now, before this becomes a post of its own, let me address the second point.
Complexity in calories
Take the case of a person who has recently come down from 250 to 230 lbs, and is attempting to lose a further 20 lbs (± 10 kg), through the use of diet and exercise. But, much to their dismay, they lose nothing. Some will say that this person has matched their calories in and calories out but not lost weight, thus discrediting the principle.
The problem is, you can never know with certainty what has happened to energy output. Until you measure it exactly (which requires complex equipment and is highly impractical), you assume that calories out is accurate. It may not be - there is a lot of evidence that muscle becomes more efficient when weight is lost, which would impact on how the estimation for energy expenditure is made. Suddenly the energy intake is again greater than it should be.
Similarly, metabolic adaptations to conserve energy have been identified. For example, a reduction in body weight (specifically, fat) causes a fall in the levels of two hormones, leptin and thyroid hormone. Problem is, when these hormone levels fall, appetite rises and metabolic rate actually goes down. If you inject leptin, incidentally, you can prevent this drop in metabolic rate (Rosenbaum, 2002 & Rosenbaum, 2005). So, referring again to the figure from yesterday (shown again below, but with the modification after metabolic adjustments), your body actually reduces the resting energy expenditure in response to weight loss, which may create an energy surplus.
This is yet another reason why I don't advise the approach of counting calories to try to match the two sides - your body is too smart, and too complex for that in the longer term! Trying to pre-emptively calculate the body's response is fraught with error, because of inaccuracy of measurement, and complexity of physiology. Yesterday, I mentioned the example of an individual who remains weight stable over a 10 year period. What I was getting at, but didn't put across correctly, is that weight balance is incredibly complex - over 9 million calories balanced in a ten-year period. That doesn't happen by accident, and it doesn't happen by preemptive design. It happens by physiology! And so losing weight requires the same principle - don't micro-manage the scale, rather be sensible and allow the theory to work for you, not to work the theory!
Final word on appetite
Then finally, something I absolutely must cover (and hope to) is the "listen to your appetite" theory. Your body is remarkable and it does signal to us when we need to rest, to eat, to drink, and even what (a salt craving for example, is part of the exquisitely regulated osmolality homeostat that sports drink companies don't want to recognize!).
However, in the case of diet, we're subjected to too many external influences that affect appetite that many people cannot rely solely on how they feel in order to eat correctly. There's some great research on this - Brian Wansink has done some studies with interesting titles like "Is this a meal or snack? Situational cues that drive perceptions.", and "How visibility and convenience influence candy consumption." He has also written a book called Mindless Eating: Why We Eat More Than We Think, detailing this fascinating phenomenon. (just a note - at the end of the series, I'll do a book list with some recommended reading on weight loss, looking at both exercise and diet)
Then there is the psychological component of food, which cannot be ignored, because our desire to eat is not simply 'physiological' in that stress and emotional cues trigger eating (we all know this as "comfort food", among other things). I would argue that these are still physiological, mediated by neurotransmitters in the brain, but this is semantics. Point is, we may not be able to trust that our body signals when to stop or to cut back. And then finally, I've already mentioned that with reduced weight (and fat mass) comes a fall in leptin, which then increases our appetites, playing havoc with the theory as our weight changes.
All in all, a complex issue, and another one to tackle in detail later (if not in this series, then in another).
So that's it for my "short" reply to your posts. I just wanted to consolidate yesterday's posts, but I guess there were a couple of key points to make. The principle of increasing energy expenditure and cutting down energy intake is without doubt the simple solution. Achieving this is difficult (but this does not make the principle wrong, take note), and there is a physiological layer of complexity that makes it impossible to preemptively manage energy in and energy out. What it boils down to is systematic sensible choice, with expert support to get the principles correct.
Part 3 on fat is on the way - probably later in the week, I have a presentation to work on first, so forgive the sudden "loss in momentum" of the series.