Food reward, a factor in obesity

 “I think food reward offers the most compelling explanation for the US/global obesity epidemic.” 

Stephan Guynet 
In studies where the food intake and energy expenditure of subjects are carefully monitored over a period of weeks to months (which tends to average out day-to-day fluctuations) a remarkable balance between calories consumed and calories burned was observed. When various mammals, from mice to monkeys, are either overfed or starved for a few weeks, their weight soon returns to normal levels when free access to food is resumed. Crucially, our mammalian bodies seem to be able to regulate feeding based on the amount of energy available in the food we consume, not just on the volume of that food.

The above quote David Linden, suggests the body controls body weight by registering the amount of energy in food. This theorizing usually leads to the white adipose tissue derived hormone leptin and particularly its effect on the hypothalamus. Leptin, in general, correlate with adipose tissue mass. But the energy the body needs comes from two places: food and stored energy. Increasing use of stored energy will make animals and human eat less. Any energy-sensing control system must register the total amount of energy available, both from foods and from fat and glycogen stores. From this point of view, obesity could to be caused by the body not having access to its own stored energy and so continues to signal for food intake. Alternatively, the stored energy is readily available, but somehow an obese person experience feelings of hunger and craving that overpower any signal telling the brain that there is enough energy available. This scenario makes it likely that obesity is caused by a malfunctioning control system.

Stephan Guyenet has created quite a stir lately with his posts about food reward. Several of the posts have over 100 comments, some more rational than others, but people clearly have strong feelings about this. I think one of the reasons some people feel personally offended by his writing, is that they feel food reward lends support to overweight being caused by lack of willpower. This is definitely not Stephan’s intent, nor does his reasoning indicate willpower as a major factor. Nevertheless, willpower is a major part of food reward, as one of the opposing forces to a physiological drive to consume rewarding foods.

The theory of food reward is a theory of how foods affect our feelings, stimulate our behavior and how some foods appear addictive and promote addictive behavior. This seems lost on many. Food reward does not and cannot explain how we fatten. To find the answer to this we need to look at the physiology of the fat cells. Basic biochemistry still applies and some foods are more fattening than others, although as it seems, Stephan does not think so and he even uses his belief that macronutrients doesn’t matter as an argument in favor of the food reward theory. But the theory itself is a theory of why we (over)eat, not a theory of how we gain fat.

Even though the theory of food reward is not about willpower, willpower invariably enters into the equation. Many physiological drives can be affected by conscious thought. Stick your hand in ice water and your head tells you to pull it out (or your spine), but you can keep it submerged by willpower, some longer than others. Highly rewarding foods do, according to Guyenet, cause obesity in susceptible people, just like drugs may make addicts of some (often the same people). Still, I cannot see that food reward argues more strongly for willpower as a part of obesity, than other rational theories.

The theory of food reward is actually mostly about carbohydrates as most of the data relating to it is from the studying of sweet foods. As Hans-Rudolf Berthoud put it 

For nonsweet palatable foods (typically high-fat foods), there is less convincing evidence for development of dependence…” [1]
So it seems the key questions are:

– do sweet foods cause addiction and increased energy intake with subsequent obesity?

or
– do sweet foods cause obesity (fat storage) with following addiction or addiction like behavior possibly caused by metabolic clues?

As we undoubtedly fatten differently and not everyone becomes obese despite similar obesogenic environments, we can conclude that addiction to high palatability foods is 1) genetic and that preexisting differences in reward functions cause obesity; 2) intake of palatable foods is in itself addictive and leads to obesity; or 3) obesity (the excess storage of energy in fat tissue) cause changes in reward functions thus further accelerating obesity.

As many lean people also eat large amounts of highly rewarding foods, it seems unlikely that the food itself can be to blame. So, either food reward is secondary to the harmful effects of sugars/grains (sweet food not found in hunter gatherers): these foods create excessive fat storage in obesity prone people and this cause addictive behavior towards the very same foods; or it is the primary cause of obesity: people prone to weight gain have physiological measurable differences in parts of the brain that cause an addictive intake of fattening foods.

Although I enjoyed the posts about food reward I was left with very many unanswered questions after reading:

The reasoning 
Stephan uses the fact that hunter-gatherers are lean in support of rewarding foods causing obesity in non HG societies, arguing that one of the reasons hunter gatherers are lean is because their diets are bland (although I think many HG’s would disapprove of their diets being called bland). This argument could go both ways. Because if the foods that drive fat gain also promote addictive intake of the same foods, then traditional diets can be as tasty as any, just as long as they do not contain these particular foods. As long as they don’t, there is no reason to think blandness is the cause of leanness.

Although lean traditional people’s diets are more unrewarding then say a SAD diet, this does not mean that we in the west become obese because our foods are not.

Also we have to ask: if obese people remove fattening foods, which are the same as those considered highly rewarding, will the addictive behavior/strong cravings for the fattening foods subside? I know from experience that many who struggle with strong cravings, lose their cravings when switching to a LCHF diet. The fact that some feel cravings even after some time on low carb diets, does not favor a set-point hypothesis. It could just indicate a dietary insufficiency, like the lack of salts or some fatty acids. As the cravings usually disappear before a considerable weight is lost, it is unlikely that the cravings were caused by the obesity itself. Often, it seems that cravings disappear when people regain the ability to burn fat.

Burning fat, or having a functional metabolism will make us eat less. The oxidation of fat in the liver offers a strong satiety signal [2]. So, even if lipolysis is high in obese, hunger will not go down if somehow the burning of fat in the liver is restricted. This is sort of a “metabolism argument”: One of the things that separate those prone to obesity and insulin resistance from the rest, is a poor and broken metabolism. They rely on glucose (glycogen) for fuel and have poor fatty acid oxidation in combination with blood sugar fluctuations and cravings, so fat is stored rather than burned as it should. Resolving the metabolism issues will in many reduce the cravings and rewarding foods are no longer an issue.

Another important question to ask is: how often during the day and how much hyperpalatable, highly rewarding foods do people who become obese actually eat?

If people become obese without consuming highly rewarding foods (something I consider very possible) then the theory of food reward argues strongly that this type of obesity is mostly due to lack of willpower, as there is no addiction to blame.

The “bland food” study from 1965 Stephan writes of can be used to support a “food reward” theory, but there are many other ways of explaining why the overweight people lost weight while the lean did, not. If the obese ate high sugar/grain and franken-fat diets, that also happen to be palatable once you get used to it, then of course they lost weight on the liquid diet.

The first volunteer continued eating bland food from the machine for a total of 70 days, losing approximately 70 pounds. After that, he was sent home with the formula and instructed to drink 400 calories of it per day, which he did for an additional 185 days, after which his total weight loss was 200 lbs. The investigators remarked that «during all this time weight was steadily lost and the patient never complained of hunger or gastrointestinal discomfort.» This is truly a starvation-level calorie intake, and to eat it continually for 255 days without hunger suggests that something rather interesting was happening in this man’s body.

This isn’t really that interesting. With all likelihood the man could have lost an equal amount of weight eating real foods that are far more rewarding but not fattening. It has been known to happen.

I think decreased fasting insulin occurs as a result of weight loss…

Stephan Guyenet 

Another important point is that the body fat “setpoint” is still a theoretical point, and any theory based on the setpoint hypothesis is equally hypothetical. 

As one would expect if food reward influences the body fat setpoint, lean volunteers maintained starting weight and a normal calorie intake, while their obese counterparts rapidly lost a massive amount of fat and reduced calorie intake dramatically without hunger. This suggests that obesity is not entirely due to a «broken» metabolism (although that may still contribute), but also at least in part to a heightened sensitivity to food reward in susceptible people. This also implies that obesity may not be a disorder, but rather a normal response to the prevailing dietary environment in affluent nations.

Lean people have good access to their own body fat and high fat oxidation rates. They have a better working liver than obese, and they definitely had a better pre experiment diet than the obese. The above results can be explained exclusively by a broken metabolism theory. There is no need to involve food reward.

Some people may be inclined to think «well, if food tastes bad, you eat less of it; so what!» Although that may be true to some extent, I don’t think it can explain the fact that bland diets affect the calorie intake of lean and obese people differently.

Most diets affect lean and obese differently. These people are per definition quite different metabolism wise, and foods affect metabolism. Once again, the fact that one of the many diets that affect lean and obese differently are bland, does not lend much evidence for palatability playing a major part in obesity.

Although the rewarding abilities of different foods might explain some of the reason we overeat on fattening foods there are very many other ways you are likely to gain weight. As David Pier points out in the comments section:

Excess fructose? Too high an omega-6/omega-3 ratio? Too much omega-6? Too little omega-3? Too much polyunsaturated fat in general? Too little saturated fat? Micronutrient (choline, minerals, etc.) deficiencies? Excess total carbohydrate? Superstimulating hyperpalatibility? Over-availability? Excess insulin (cause and/or effect)? Gut flora (cause and/or effect)? Lack of fiber (insoluble and/or soluble)? Multi-generational epigenetic changes? Artificial sweeteners? Endocrine disruptors? Sleep disturbances? Psychological causes essentially independent of all hormonal homeostatic mechanisms?

In his third post, Guyenet writes about the review of low fat non energy restricted diets where overweight lost more weight than lean:

In other words, low-fat groups reduced their calorie intake by an average of 271 calories per day, and lost 7.5 pounds (3.2 kg). When they considered only people who started off overweight, they lost 12.8 pounds (5.8 kg). The investigators noted that the results were similar no matter what the duration of the trial, because weight loss plateaued fairly quickly.

Then he writes

This is all without any instruction to reduce calorie intake, therefore we can assume these dieters were eating to fullness.

No you can’t assume that. These are participants included in non blinded weight loss trials. I would say it’s a safer bet that they were in fact restricting their food intake.

The best low-carbohydrate diet study I’ve seen was published in 2008 in the New England Journal of Medicine (3). 322 «moderately obese» participants were placed on a low-carbohydrate diet, a calorie-restricted low-fat diet, or a Mediterranean diet, for two years. The low-carbohydrate group’s carbohydrate intake decreased by 130 grams per day, which is about half of a typical person’s total intake, and neatly corresponds to the reduction in calories of 561 per day, despite not being instructed to reduce calorie intake.

At two years, the low-carbohydrate group had lost 10.4 lbs (4.7 kg), which is very similar to the average weight loss seen in low-fat diet trials.

There are two major issues here. 1) The study by Shai et al is a horrible study: The Atkins based diet came with recommendations of getting fat from vegetable sources; By 24 months, carbohydrates constituted 40% in the low carb group and 50% in the low fat group. The low fat diet went from baseline fat intake of 31,4% to 30% (no reduction at all); the aurhors left out baseline energy intakes and only reported reductions; The study also used intention to treat analyses. The weight loss in the low carb group for the 272 who completed the study was 5.5kg in the “low carb” and 3.3kg in the “low fat” group. After 6 months the study diets were not very dissimilar.

If this is the best low-carbohydrate study Guyenet has read, he needs to read the other studies. Low-carbohydrate diets usually outperform low fat diets, as long as carbohydrate intake is kept restricted. This outperformance is despite low fat groups having caloric restrictions while low carb groups can stuff themselves as much as they want. His reasoning that low carb and low fat perform equally is flawed in so many ways, and he uses this reasoning to support a food reward hypothesis.

I think the reason very low-carb ketogenic diets cause fat loss is the same reason extreme low-fat diets cause it: they have a greatly reduced reward value.” 

Stephan Guyenet 

The fact that participants in the Lindberg study lost weight without caloric restrictions does not mean food reward had anything to do with it. Once again, if certain foods themselves cause fattening, and we restrict these foods, weight loss is likely to occur. There is no need to blame blandness.

Messing about with dopamine signaling can cause obesity in animal models, and there are differences in dopamine receptors between «normal» people and those prone to addictive behavior. It is not strange that messing about with the brain will cause all sorts of things, but it does not mean obesity is caused by food reward.

There is more reasoning to discuss, but this post is getting way to long. Is there really enough available evidence to justify calling food reward a dominant factor in obesity? If there is, I can’t say I found evidence of this in Stephan’s posts.

And as Paul Jaminet pointed out:

Likewise, we’re all familiar with young people who eat massive quantities of junk food and remain slender. The high food reward diets, even toxic and malnourishing diets, seem not to cause weight gain until some kind of metabolic damage occurs.

It seems that metabolic damage – the disease of obesity – is a prerequisite for food reward to matter.

Obese people should eat boring diets
Guyenet even offers tips on how to make food less palatable and more bland. But does this mean that there are people out there who have tried all the obvious ways to lose weight, like reducing inflammation and cutting back on carbs, who have not succeeded and are left with trying to make food not taste good?

The most palatable foods are those packed with fat and sugar. These foods are the first to go on any dietary strategy. Do we need to make the rest of the diet bland?

Guyenet offers a range of advice for losing weight based on food reward theory. For example:

Don’t snack. In France and many other countries with strong food traditions, snacks are for children. Adults eat at mealtime, in a deliberate manner.

And yet, if snack in itself do not seem to cause obesity, why not snack?

Don’t add fat to your food. That doesn’t mean don’t eat fat, it just means keep it separate from your cooking. If you want to eat butter, eat it separately rather than mixing it in with your dish.

…I don’t know what to say about this…but I know I don’t like it.

Some of his advices are meant mostly for those who struggle to lose weight, but I fear if anyone would follow them, they would die of boredom instead:

Eat only single ingredients with no flavorings added. No spices, herbs, salt, added sweeteners, added fats, etc. If you eat a potato, eat it plain. If you eat a piece of chicken, eat it plain. It can be in the same meal as other foods, but don’t mix anything together. If you would like to keep salt in your diet, dissolve it in water and drink it separately.

There are more of course. Most make sense, but they also make sense without considering food reward.

Importantly, all the studies used to support the award theory can also be used to support different theories. While they do no not falsify a reward theory they do not provide strong supportive evidence. But this is how science works. Stephan is right in offering the theory and he might turn out to be spot on. It will be interesting to see what future studies will reveal. We need some RCT’s to enlighten the causation between food and dopamine response and function, well any kind of RCT in this field would be important. I would like to make foods that are highly rewarding (measured by dopamine response or something fancy, that make people crave them, and that does not contain anything inherently fattening. Then I would give people free access to it to see if they got fat. Wonder what it could be?

«Some people have lost fat simply by avoiding carbohydrate or fat. I’ve heard people say that a low-carbohydrate diet in particular curbs their cravings and allow them to have a healthy relationship with food again (although others have developed strong cravings on low-carbohydrate diets). I believe this is mostly, if not exclusively, driven by the fact that carbohydrate and fat are major reward factors.»

Stephan Guyenet

References

1. Berthoud HR, Lenard NR, Shin AC: Food reward, hyperphagia, and obesity. Am J Physiol Regul Integr Comp Physiol 2011, 300: R1266-R1277.

2. Friedman MI, Harris RB, Ji H, Ramirez I, Tordoff MG: Fatty acid oxidation affects food intake by altering hepatic energy status. Am J Physiol 1999, 276: R1046-R1053.

10 thoughts on “Food reward, a factor in obesity”

  1. Very Good.
    I liked his «food that causes inflammation raises your weight set point» better.

    At least it explains why the paleo diet is so successful for losing and keeping weight off.

    We eat delicious dinners both at home and restaurants and my weight has been stable for a year and my wife's weight has remained stable for 5 years. Previously she lost 50lbs and I lost 32lbs. We are rarely hungry. We just eliminate all non-paleo foods and eat less than 100 grams of carbs a day.

    The true test of Stephan's theory is our recent two week trip to Florence Italy. We had great meals every night in the better restaurants of the city. We did not limit portions. We just followed paleo rules. At the end of the two weeks, I had lost a pound and my wife's weight was unchanged.

    So Stephan's theory was certainly wrong in our case.

    Liker

  2. It's incredible how people have to find strange solutions to a problem a lot of people already have a very easy and straightforward solution for. Talk about trying to re-invent the wheel….

    Liker

  3. Hi Pal,

    Very nice discussion.

    I would also be interested in RCTs. Since our diet is so similar to Stephan's, but for blandness and food reward, it would be great to compare them. I don't know which would do better for weight loss, but I'm sure ours would do better for compliance!

    Best, Paul

    Liker

  4. Hello Pal,
    I'm glad PHD pointed me to this discussion of Stephan's theory. You make many valid points that help me put his theory into perspective and put spices into my meals! I've been «crazy spicing» for several years based on Seth Roberts' theory and enjoy never eating the same meal twice.

    Liker

  5. I think that there could be more than one reason for obesity. Obviously carb restrictions aren't working for Jimmy Moore

    Liker

  6. mfairchild: food without spice is not food, just nutrition.

    Anonymous: Of course there is more to obesity. Proper liver function is key. Low carb does help, but is not sufficient. Potential infections and nutrition deficits should also be looked into. The fact that one person does not succeed on low carb does not mean low carb is the problem. If you read Jimmy's blog you'll find that he elaborates on his weight loss battle.

    Liker

  7. Interesting rambling.
    I wish you could clarify the ideas of reward and palatability. In Stephan's case they are not interchangeable although his recommendations indicate a bland diet might be necessary for problematic cases. What we find bland in the 'West' is not bland for the people who haven't tasted our food, or haven't had access to so many processed foods or 'treats' in their childhood. Stephan's bland diet definitely looks boring for me and I have problems eating the fat on its own. But it reduces my appetite. I couldn't finish three unsalted baby potatoes, two boiled eggs and a piece of lamb's liver the size of my palm. I had to force myself to eat the second egg and left the third potato in the lunch box. Today we had roast chicken, roast potatoes with gravy and peas with butter for dinner. I finished a leg, 4 baby potatoes, the peas, consciously left the skin and tried not to eat too much butter, but I got up looking for more. I didn't, but it was a conscious decision.
    I agree that the bland diet doesn't make you forget the very palatable foods, the ones to which you're addicted if you are, maybe it is more to do with your resolve to keep doing it rather than with your vanishing cravings. Or the cravings become more cerebral rather than physical. I think so. I couldn't go through the day without sweet chocolate before and now I don't even look at it in the shop.

    Related to the rewarding aspect of fat, I find thick double cream totally addictive. What does all this say about my metabolism? (I'm not trying to criticise VLC diets, I did VLC for 2 and half years but I stopped loosing)
    Thanks.

    Liker

  8. Hi lightcan
    I think reward and palatability is to sides of the same, and it seems that Stephan is using the words somewhat interchangeably. Palatable food is rewarding and more palatable foods are more rewarding. In the end, reward is a theoretically measurable dopamine response. The response, I would assume, is also affected by our experience so that foods that come with good memories is more rewarding that those without. But part of the reward feeling is also purely physiologic so that some foods are perceived universally rewarding and across cultures. I think a resolve to abstain from certain foods might very well resolve cravings. The brain gets good at what it does. Thinking in a certain way makes you good at thinking that way and different kinds of thought becomes harder. But thought patterns can be changed by exercise. Conscious thought also enters into the reward equation, the question is how much. I don’t know about your metabolism, but my experience is that too little fat (or carbohydrate) will make us look for more food even right after a meal and even though we are not actually hungry. I think this craving is for fat in particular. Fat is needed to have a good fat metabolism so it makes sense to eat fat. But this does not necessarily mean very low carb.

    Liker

  9. Stephan's series helped me see what others may find obvious. There are certain foods which I'm sorely tempted to over eat. Others, not.

    I love omelets with salsa, but I'm not going to get up from the table after breakfast and fix myself another one! However, if someone offered me a gluten free muffin or cookie after my omelet, the game is changed. I'd feel the urge to scarf it down and I'd be considering having seconds.

    Real Food does not light up my brain and cause me to want MORE, beyond appetite.

    I have to be careful with nut butters, chocolate, and heavy whipping cream too.

    Another thing I took away, tangentially, from Stephan's series is the idea of not having so many food choices at our fingertips. Just the idea that I can ask myself what I feel like having for any particular meal is so different from previous generations.

    I do better if I plan home cooked meals for the week, and have that in-the-moment «what do I feel like eating» part of me take a back seat.

    Liker

Legg igjen en kommentar

Fyll inn i feltene under, eller klikk på et ikon for å logge inn:

WordPress.com-logo

Du kommenterer med bruk av din WordPress.com konto. Logg ut / Endre )

Twitter picture

Du kommenterer med bruk av din Twitter konto. Logg ut / Endre )

Facebookbilde

Du kommenterer med bruk av din Facebook konto. Logg ut / Endre )

Google+ photo

Du kommenterer med bruk av din Google+ konto. Logg ut / Endre )

Kobler til %s