At 14:12 you can see the diagram of one meta-analysis which assessed whether there is the body of evidence that physical exercise helps in losing weight. Dr Lustig presented it in a very simple manner - not saying how long the exercise lasted, what the exercise actually was, how many calories equivalent it was to balance a daily energy intake, and so on. I accept that it was not possible as the claim was based on a meta-analysis - pooling together various studies and looking at the evidence in a broad manner. However, all these factors matter in evaluating why something like this works and why not.
And that is exactly my point here. WHY exercise does not work to curb down the obesity levels? They say there was a small weight loss overall and it was presented as a negligible effect. Nothing was said about whether the people had also their diet altered or not and what their diet consisted of, in general.
Let me put it this way: when you are obese and constantly gaining weight because you consume over 1000 kcal more per day than are your actual requirements for that body size and lifestyle, how long you have to exercise to burn this extra energy plus some more to achieve the weight-loss?
Here is a brief overview where you can find that if a 68 kg weighing person performs light aerobics, within a half an hour they burn mere 120 kcal. That is not even half of a regular Mars bar in the UK! With the higher body weight the energy expenditure is higher, true, but is it that much? 120 kg heavy person burns around 200 during for the same time doing the same activity. Still not a regular Mars bar, which contains 260 kcal. How much was that burger? Over 1400 kcal.
How long DAILY can you expect an obese person to perform even the light exercise? Not for 3.5 hours to burn off that extra burger calories, would you? And this is every day because they tend to overeat every day, some even double or triple the average energy requirements (extra 2000-4000 kcal) as I have seen in my favorite series Supersize vs. Superskinny. Watch it, it is eye-opening. Available on Youtube.
Any wonder why the exercise showed such a small result? And this is also why the first law of thermodynamics seems not to work here - because in such a high energy intake you cannot expect a weight loss if the energy output is not exceeding it. Moreover, it needs a substantial amount of time to achieve significant results, which most of such studies do not have. They usually assess the participants over several weeks or a few months at their best.
Therefore, the things have to be looked at from the whole perspective, not just looking at the data and dismiss this or that saying that exercise does not work. It works, in its own meaning - if people do not lose much weight, they at least do not gain as much as they would without the exercise, am I right?
The little success (half point of BMI as Dr Lustig said) actually has proven that the exercise works, but it has to be accompanied with dietary changes as well. From that slide it is not obvious whether the exercising people also had changed their diet.
It is generally easy to overeat when the food is so cheap, processed and palatable. Cheap processed food is very energy dense, which means that per 100 grams you can get much more calories form the processed food than from the unprocessed, such as fruits and vegetables. And these calories are not always only sugar, most of the time there is more fat calories than sugar calories. Add little salt and you have got a deadly trio that has the potential to make people addicted to this particular diet.
Moreover, the exercise has been found to be very effective in decreasing the risk of metabolic diseases such as type 2 diabetes. In fact, the exercise alone was found to be even more effective than the dietary changes alone. Surprised? I am not. It has its rationale based on our physiology. It is very simple: when you over consume, you store the energy not only in the fat, but also in the muscles and liver up to a certain point as their storage capacity is limited, unlike for the fat deposits.
Especially the muscles are responsible for the most of the insulin mediated glucose uptake in the body. When you overeat and have a sedentary lifestyle or remain bed bound for several days, they are kept in the 'full of energy' state during the day and cannot take in any more. In excess, the glucose, instead of refueling the muscles, keeps circulating in the body and the body keeps producing more insulin to fit it somewhere as it should not stay in the blood in high concentrations. That leads to hyperinsulinemia.
Humans have quite a low capacity for the de-novo lipogenesis (DNL) as you could see elsewhere. There are other processes that happen in such a hypercaloric state but this is the main mechanism. Once the person starts exercising, the muscles burn the energy they have and start taking in more again which results in the drop of a high blood glucose and also blood lipids. And since high levels of insulin are not needed anymore, insulin drops down also. That's it!
We, as a species, have evolved being physically active and that is the need of our physiology today, too. Stop being active and the consequences come. Plug the hole in the sink and it will soon overflow. As long as one or two days of being bed bound with excessive eating can lead to the changes in our biochemistry indicating a pre-diabetic state. Keep doing the exercise while overeating and you will just keep gaining weight while you will most likely remain metabolically healthy for a pretty long time. Just please do not take this as my approval to overeat, OK? Healthy weight also matters.
And finally: look at the diagram above again. The plot contains the results of different studies. Some worked, others did not, when examining the effectiveness of exercise on the weight management. It was only the overall figure of pooling all these results together that Dr Lustig presented as the small and negligible difference. At least the three studies (towards the left from the vertical line expressing that mean results) showed quite a success, did they not? I would have to look at each of them individually to give you a full report what made them show the effect and why other studies failed to do so. But even from this you can see that it really depends on the circumstances whether the exercise works or not. The first law of thermodynamics still applies here and the exercise DOES work when the energy output exceeds the energy input in a persistent and more permanent manner.
One more thing I have noticed when listening the lecture further at the minute 18:55:
Look at the right column Activity. So, if the lowered level of activity has contributed to the obesity epidemics and associated metabolic diseases in children, why suddenly the physical activity does not seem to work, according to Dr Lustig? Yes, he did question this aspect and went for the usual toxic substance (fructose) in our diet after that but it is generally accepted in the scientific community that physical activity does play a role in the weight management and overall health of people and it is usually advised and promoted by the health authorities and implemented into the government policies, too. Dr Lustig provided no sufficient evidence that the physical activity is negligible or does not work in maintaining a healthy body weight, except of the meta-analysis study mentioned earlier.
To be on a neutral side I must say that other studies also concluded that the exercise has little impact on weight loss and the change in the diet produces a higher effect, but this was only because of the insufficient balance of the calories I have discussed above. It is more effective not to eat that chocolate cake than trying to burn it off.
I know it from myself: I have been maintaining a lower body weight for some time now, with tiny fluctuations in one kilo up or down. And I know that when my physical activity suddenly increases for a couple of days while the diet remains the same and balanced, my body analyzing scales notice this with a couple of dekagrams and also estimate a lower percentage of body fat in my legs while increasing the percentage of water and muscles. I need no further evidence that the exercise works. I assess my body composition quite regularly, I maintain a record and do it at pretty constant conditions. The measurements were also consistent all the time.
And here I come to the last point of this article: there is a difference between maintaining a healthy body weight and reducing the body weight of obese people. These two premises are quite different, because when you are of a healthy weight, it requires less effort from you to exercise and you also need to exercise less to keep the energy in balance. For obese people this is particularly difficult to do on a regular basis and the drop-off rate is also very high, which contributes to the failure of such programs. What may be a light aerobic for a fit person, for an obese person it can become quite a burden after 5 or 10 minutes. Now imagine them doing this for an hour to merely burn the single Mars bar...
But, as one large supermarket chain advertises: 'Every little helps', the burned 120 or 200 kcal means they were not deposited in the fat stores and the muscles are now ready to take more glucose and more fat from the blood stream. Remember Dr Lustig saying that obesity is not a problem and that 20% of obese people are metabolically healthy? Well, 80% are not and physical activity has a huge potential in helping them out of this doom. He also admitted this in another video at 1:18:05 time that he has been struggling with his high body weight and the diet, but that the constant physical exercise helps him to reduce the abdominal fat deposits.
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