Why Is Weight Loss So Difficult – A Scientific Explanation

A few weeks ago, I had the pleasure of going to a Smithsonian sponsored talk by Dr. Hall, who is a Senior Investigator at NIH and chief of one of the research programs at the National Institute of Diabetes and Digestive and Kidney Diseases that reaches across different branches of the institute. It was the first talk in a series called “Pulse on Modern Medicine”.

The NIH Clinical Center is the largest hospital in the U.S. devoted strictly to biomedical research. Dr. Hall’s particular interest is how the brain adapts to changes in nutrition and exercise. He addresses weight loss not as a cosmetic issue – i.e., can you zip your jeans – but as a risk factor for heart disease, diabetes and other chronic diseases.

His graphs demonstrate that there was a 20 pound average weight gain per person over the 20 years from 1985 – 2005. This corresponds to consumption of 200-300 extra calories per day. The food production in this country over that time increased even more – we could have been even MORE overweight by now. Production excess can be attributed in part to improved agricultural techniques and subsidies for some higher calorie crops. But sadly, as discussed in a prior article, 40% of food grown does not get eaten. It is wasted either by not being harvested, being damaged and not marketable, never arriving at a store, or getting to the store and either being refused or not being purchased. In total, two thirds of the increased food produced goes to waste, while 1/3 contributes to obesity.

Dr. Hall argues that the changing food environment and cues account for much of the weight gain. There hasn’t suddenly been a global lack of willpower, he argues. Much of the food consumed is very processed. We snack more, go out to eat more, and ‘heat’ or ‘microwave’ instead of cooking whole foods at home.

He showed a montage of the many, MANY diet books. Each of the 50,000 theories and books that vie for your attention is based on a thread of truth. For instance, the low carb argument is that carbs induce insulin release, which increases fat uptake. That’s true, but studies show that insulin secretion doesn’t predict which diet would help someone lose weight. Good theory, but not borne out scientifically. One of the newer insulin medications, canagliflozin works in part by allowing sugar to be excreted in the urine. Blood sugar goes down, and you would think, weight would be lost based on all the sugar that is leaving the body. One study found that only a relatively small amount of weight -10 pounds – was lost over long term use. People evidently ended up consuming 100 calories per day more for each kilogram of weight that was lost, so they eventually reach a new equilibrium.

All the diet books that argue that you can lose weight with low carbs, low fat, or anything else, generally depend on your consuming fewer calories by adhering to their diet. So people can lose weight with any one of them. But no matter what is claimed, there is no one good diet for anyone. The best nutrition plan is one that you can comfortably stay with, that contains whole unprocessed foods – fruits and vegetables, whole grains, and lean protein including nuts and beans. This hasn’t changed in decades.

However, Dr. Hall does NOT say that weight loss is plain and simple – just eat less and you’ll lose weight. In fact, he presents just how complex the situation is, based on studies.

He argues that obesity is at least in part a brain disorder. The brain controls the changes in eating behavior in a particular environment. Increased availability of poor food choices drives eating. This is an opportunistic behavior based on what is in view. It is not driven by hunger. With some addictions and pleasurable activities, dopamine increases in the pleasure centers of the brain. With eating these foods, particularly in people with higher BMI, dopamine, increases in the ‘habit forming’ areas. BMI (body mass index), is a relationship of weight to height).  

He demonstrated how even the medical community is out of touch with reality. For years, we have been saying that if you cut 3500 calories per week from your usual intake, you will lose a pound each week. To disprove this he showed a comical graph in which a person would eventually disappear over time by maintaining this lower calorie intake. Instead, decreased calories eaten gradually leads to decreased calories burned, so weight loss does not continue at the same rate. If we want to make sense of this, think of our former hunter-gatherer selves. If food was scarce, our bodies would cleverly conserve calories or energy. The decrease in calories burned, or lower metabolic rate, contributes to the usual weight GAIN that follows weight LOSS.

The calories burned at rest just from the work of living is called the resting metabolic rate or basal metabolic rate, RMR or BMR. It decreases as you lose weight, and stays low even when you start to regain, therefore making it more likely you will regain what you lost, and maybe even more. Not fair, right?   There is particular risk for heart disease when excess weight is concentrated in the abdominal area.   Dr. Hall noted that 40-70% of the body habitus is dependent on genetics.  Rather than trying to lose weight in one area, overall weight needs to be reduced.

He used The Biggest Loser contestants as models of what happens with extreme weight loss. They go to a program with reduced calories and marked increase in physical activity, enough to lose a pound a day. With hours of vigorous exercise, they burn over 2000 calories more than they did before. But, their metabolic rate DECREASES to the tune of 800 calories a day. They still DO lose weight, due to an extreme decrease in calories eaten and extreme increase in calories burned – a program that can’t be maintained forever. On average, they lost 60 kg each …. and regained 40 kg. But, this still is a net 13% weight loss, which is better than the 5-10% we usually aim for.

Overall, caloric intake seems to predict weight loss more than a change in physical activity does. But LONG TERM, increased activity is a better predictor of maintaining the weight loss. For the ‘losers’ noted above, those who continued with exercise that was 150% compared with baseline kept the weight off. For the group as a whole, over 80% of the weight loss was body fat, not lean body mass, which is good. Lean body mass is important for maintaining strength.

So if metabolic rate slows after weight loss and doesn’t necessarily increase again with time, how can a person be successful with weight loss? Here are some takeaway messages:

* Physical activity is key – it must be maintained at a high level.

* Cues and triggers to poor eating must be avoided – that may mean making sure snacks are not available at home or are very inconvenient to get to; you may have to change how you walk to the metro to avoid Starbucks, Dunkin or other places.

* Expectations need to be reasonable, based on all this information, to avoid the sense of failing. Now there are scientific explanations for why significant weight loss is very difficult and weight re-gain is likely.

* Avoid the latest fad!

* Dr. Hall suggested using the Body Weight Planner to help manage planning and expectations. 

Attendees asked questions about the timing of food intake, intermittent fasting and the importance of the human micro biome regarding obesity. The jury is out. These ideas are being explored in rodents, but so far we don’t have useful information on humans. Dr. Hall explained the difference between an explanation that makes sense, based on logic or animal data, and a scientific theory that has been tested with trials. We have to be careful not to confuse the two, or be fooled by the 50,001st diet or cookbook that is published.

Eat healthfully and keep moving – my two cents! There are benefits that accrue from fitness, with or without weight loss.

REFERENCES: 

Link to Body Weight Planner : https://www.niddk.nih.gov/health-information/weight-management/body-weight-planner