When reviewing the literature it seems that many people are experts in clinical nutrition (meaning that they are helping other people to control their weight), and also many people are experts in biochemistry and metabolism, but the overlap is very narrow, especially in the academic world. It is my impression that the only people who really bridge this gap are practitioners and multidisciplinary experts like Gary Taubes and Mark Sisson to name just two.
This is important. Given the complexity of the human body, and our still limited knowledge about it, one can draw many conclusions that are perfectly logical – and nevertheless wrong. So if one wants to develop a diet to lose weight, one can not simply go to the drawing board in the ivory tower and at one point finished product pops out and they all lived thin and happily ever after. Like in any applied science, one needs to develop a method, test it against the data available, then create an actionable plan, implement it and see if it works consistently. This is hard work, and expensive. And it has a strong human component (“Do people follow the instructions?”) that one might not be comfortable with.
To cut a long story short – my money is on the guys who have worked with people to lose weight, and who know just enough about the biochemistry involved, rather than the the-earth-is-flat experts who have never set a foot on a ship.
The classic paradigm of weight-loss is what I want to call Calories-In/Calories-Out (or “CICO“, which sounds much cuter). CICO is based on the thermodynamic principle of conservation of energy, which implies that
energy stored = energy provided – energy expended
and gives an easy recipe for losing weight: either eat less, or run more, or both.
The other – and newer – paradigm is what I’d call the It’s The Insulin, Stupid (or “ITIS“) paradigm, which (in gross simplification) states that the energy balance (CICO) does not reallt matter, and that it is the insulin (and other hormones) that determine whether we gain or lose weight. The recipe for losing weight here is to control one’s insulin levels and – as far as possible – the insulin sensitivity of the (fat) cells, which first and foremost is done via controlling the carbs.
In line with what I have said before, using pure logic both of those paradigms seem correct. CICO is pure thermodynamics, so it must be true, right? The short answer is: “Not really”. The long answer is that whilst the equation holds per se, energy expended is not an independent variable. In particular, the body has a number of means to adjust it as a function of energy provided. You eat less, you get tired and stop moving. You eat more, the body burns off the excess energy. Body fat remains the same.
The ITIS paradigm is more difficult to invalidate – if only because it is notoriously difficult to measure hormone levels and -sensitivities inside a living organism. It has a number of powerful arguments going for it though, eg mice who became undernourished (lethargic, losing muscle) whilst building up fat when their hormone balance was altered (this, and many more examples, are in Gary Taubes book “Why we get fat”).
My personal take on this is that both paradigms are right to some extent, but that ITIS is more important in practice. CICO applies if we consistently and seriously over- or underprovide calories. If we eat nothing, we lose fat (and muscle, and other organs for that matter), and if we drink a liter of olive oil over and beyond our maintenance calories we will probably gain weight (albeit not at a rate of about 1kg per days as CICO would imply).
However, in the normal zone – and this is where we should strive to be – in my view ITIS applies, or at least dominates. The important (and not at all obvious) implication is that
For weight-loss it firstly matters what you eat. How much you eat is only a secondary consideration!
But I am getting slightly ahead of myself here. The step that is missing is that insulin (and other hormones) can be effectively controlled by the composition of your food – and if you look at it quite a few of the modern diets go along those lines
- The Atkins Diet reduces carbs in general (replacing it with lean protein), thereby limiting insulin response
- The GI Diet (and the Southbeach Diet) focus on using good carbs (those that have a low glycemic index, meaning they are digested slowly) as they avoid insulin spikes
- The Zone Diet prescribes a fixed macronutrient ratio (typically 40/30/30% of calories from carbs/protein/fat) to be maintained at each and every meal in order to minimize an insulin response
- The Paleo and Primal diet(s) eliminate all grains (and starches), thereby seriously limiting the amount of carbs; contrary to the Atkins diet, fat is considered to be good (some fats at least)
- Ketogenic diets mainly or completely remove the carbs from the diet, making the organs that usually run on carbs (brain, heart) run on ketone bodies (produced in the liver) instead
It is worth noting that neither of the above “diets” is a diet in the common sense of the word – it is not something that you “go on” when you want to lose weight, and “go off” once you are done. Each of those diets (arguably with the exception of the last one, which could be relaxed into any of the others) is meant to be maintained throughout life.
So how does this work in practice?
At the risk of repeating myself, I will be slightly rehashing the above in order to better explain what – in my personal understanding – is the middle-of-road view of nutrition, diet, and metabolism.
The chief reason why fat is stored in the fat cells is because insulin levels are high at a time when fat or carbs are in the bloodstream (ITIS). Conversely, fat from the fat-cells can only be consumed by the body when insulin levels in the blood are low.
The implication is that in order to lose weight, one should strive to keep insulin levels low, which means that that carb intake should be carefully controlled. Details differ. Some say that only the peaks (and therefore troughs) of the insulin level need to be controlled, which means that carbs are generally OK, albeit of the low GI variety and/or in conjunction with protein – this is the GI/Southbeach/Zone view. Others say that carb intake needs to be seriously reduced – this is the Atkins/Paleo/Primal/Ketogenic view.
One exception that some people of all ideologies are making is that the rules for post-workout nutrition differ: if the glycogen stores in the skeletal muscles and/or the liver are low, then – even in the presence of insulin – carbs in the bloodstream are stored there rather there than in the fat cells. So it seems there is a window (of about 30-60min) after exercise where high carbohydrate intakes – including of sugars – do not lead to a build-up of fat, but rather to a faster recovery of the all-important glycogen stores.
Where the different ideologies do not agree is what should replace the energy that would have otherwise been provided by the carbs. Some (eg Atkins, and to some extent Zone) rely heavily on proteins. Others – in particular Paleo / Primal – want to limit the protein intake to what is necessary to maintain/build muscle, and use fat as the main source of energy. It should be noted though that the protein levels required can nevertheless be quite high – Mark Sisson speaks about 0.5-1g protein per kg of lean body mass, and some more body-building focused publications double that. So for me for example at about 100kg this means that I need to consume between 100-200g of protein per day, which corresponds to 400-800cals already.
My personal view on this is more along the lines of the Paleo/Primal folk: I believe that it makes sense to get the extra calories from fat rather than from protein, for a multitude of reasons. Firstly, it seem intuitive that if you want the body to burn fat you need to make sure that it knows how to do so. There is also a sustainability (and cost) argument: it is much easier and cheaper to grow olive groves than it is to rear grass-fed cattle, the latter being arguably impossible for mankind as a whole. And if one decides to rear cattle, then at least all of it should be consumed, and the most nutritious part (the fat) should not simply be thrown away.
After we have tackled what we should eat, it is now time to address how much of it we should eat. Again, different camps have different views. Some – eg Dr Sears of Zone Diet fame I believe – essentially advocate “as little as reasonably possible”, on the basis that (a) the whole digestion process puts stress on the body, (b) the intake of potentially toxic constituents is reduced when eating less, and (c) last but not least that the body learns to become more efficient. Other – eg Mark Sisson of the Primal Blueprint – seem to be less fuzzed and might even tell you that you can eat as much as you want (even though there might be an implicit assumption that on the right diet you would automatically keep your calorie consumption within reasonable levels).
Others – especially those of the body-building or weightlifting camp who want to build muscle – advocate eating at lot during the “bulking phase” (maybe 5000-8000cals or more per day), with the understanding however that this will lead to a build-up of fat along with the muscle, which needs to be addressed in a subsequent “cutting” phase.
The middle of the road view is probably to at least get a feel for one’s calorie needs – ie one’s basic metabolic rate, plus whatever one needs for activities and sports – and then structure one’s calorie intake around it. My feeling is that in the higher carb diets (eg Zone, GI, Southbeach) it is very important to monitor overall calorie intake (and to reduce it accordingly when trying to lose weight), whilst on the low/no carb diets (eg Paleo/Primal, Ketogenic, also Atkins) the amount of calories consumed is less critical, as long as it is within reasonable bounds.
 I will on purpose ignore the topic of insulin (in)sensitivity here because it adds an additional layer of complexity, but it is worth reading up on this.