Why Most Doctors Are Wrong About Obesity Management

We all know that obesity is harmful, and that weight-loss is difficult. This is frustrating for GPs and for our patients. However, I believe this could be avoided easily (because most doctors still manage obesity based on opinion rather than on evidence)…

Just have a look at the following easy-to-read summary of the key studies. While I don’t expect to fully change your mind, I hope to challenge your thinking and to offer you an interesting read. Let’s start…

Note: some of the following ideas were published previously in my review of obesity management guidelines¹ and in my articles in the Lancet² and NEJM^3,4. In April 2024 I had the honor to present this topic as a keynote at the European Young Family Doctors’ Movement:

1. Why is obesity management frustrating? Because we ignore the evidence.

My approach to this article is simple. I tried to answer the most relevant clinical questions with the best available research evidence. While there are thousands of studies on obesity, here I tried to select – if available – only the most robust study designs:

• Systematic reviews rather than single studies (to avoid ‘cherry picking’).
• Intervention studies rather than observational studies (to assess causality).
• Long-term studies rather than short-term studies (to be more relevant).
• Clinical outcomes rather than intermediate outcomes (to be more relevant).

In other words, instead of citing some studies which confirm what I already believe, I just show you the key studies (all of them; if I missed any, please send me an email). Importantly, the results of these studies clearly indicate that our usual obesity managing is wrong…

2. What causes obesity? Not what common knowledge tells us.

Is obesity caused by lack of willpower (or even lack of intelligence)?

To be honest, I know that many (most?) of my medical colleagues believe this causes the rise of obesity:

It’s almost certain that lack of intelligence cannot explain the rise of obesity. Why not? Have a look at the following graph which shows that intelligence increased quite a lot in the last century, which is called the “Flynn Effect”:

Can willpower explain the rise of obesity? No. Why not? Just look at the following graph, and ask yourself:

• How could willpower explain the sudden rise of obesity in the mid-1970s in the USA?
• How could willpower have declined in both sexes and in all age-groups simultaneously?

There are no good answers to these questions. It seems much more plausible, that (sudden and nationwide!) changes in the food environment like the US farm bills in the 1970s – which increased production, availability, and affordability of energy dense food – led to the rise of obesity.⁵

Is obesity caused by bad genes?

Well, it depends. As genes don’t change rapidly, also they cannot explain the previously mentioned rise of obesity in the USA. However, the following graph (which is crucial!) suggests that genes can largely explain why some individuals are obese and others are not:

The underlying study⁶ is based on 290,000 UK Biobank participants and calculated 2.1 million common gene variants. It shows that having the “worst” vs the “best” genes increased the likelihood of severe obesity 25-fold (!), of obesity 4-fold, and it increased the average weight by 13 kg. However, despite these strong associations, genes are not destiny, as 17% of those with the most disadvantageous genes still have a normal weight and most (56%) are not obese. Lifestyle is still important, but definitely not everything.

Additionally, a recent review in the journal Obesity⁷ concluded that even 70%-80% of weight variance might be genetic (according to twin studies, while adoption studies and nuclear family studies yielded lower values; another review⁸ had similar findings). Most of this genetic risk is spread over many different genes, as more than 1,100 gene loci for obesity were identified by 2020.⁹ However, also single genes can be important, like the FTO gene, which controls the hormone ghrelin and thereby hunger. Variants of this gene are carried by one in six European men and increase the obesity risk by 70%.¹⁰

While not about genes, here I would like to mention another cause of obesity which is also (generally) outside of our control: gut microbes. In 2023, one Nature review concluded that “we now understand that the gut microbiome profoundly impacts energy balance through diverse mechanisms”¹¹ and another stated that “gut microbiota exert direct effects on the digestion, absorption and metabolism of food and affect body weight by modulating metabolism, appetite, bile acid metabolism, and the hormonal and immune systems”¹².

In conclusion, the obesogenic environment determines the average weight of a society and thereby the “rise of obesity”, but genes and gut microbes largely determine if your weight is above or below the average. As Philip F. Smith (NIH) said beautifully, “obesity is 80% genetic and 100% environmental”. That’s key for understanding the causes of obesity.

3. How to manage obesity? Most GPs offer ineffective interventions, and neglect effective ones.

Losing weight by eating less. Or not?

If the first law of thermodynamics is still correct, then nobody can gain weight without eating more than you expend. Calories in, calories out. However, this does not necessarily mean that telling patients to “eat less and exercise more” is an effective advice for weight loss. Why not? It’s just not as logical (and neither practical nor evidence-based) as it seems…

Let’s calculate it. Someone is overweight by 20 kg. He gained this weight over the last 20 years. How much was he overeating per day on average?

• 1 kg body fat has 7,700 kcal
• 20 kg body fat have 154,000 kcal
• To gain 20 kg body fat in 20 years (7,305 days), you must overeat only 21 kcal daily!

Can you estimate your today’s calorie balance with a precision of 21 kcal? Or of 210 kcal? If you cannot, then “having a negative energy balance” is not a practical approach. Also, to calculate your “energy balance”, you would need to know your energy expenditure, precisely. I put my own data into the online calorie calculators of NIH¹³ and Mayo Clinic¹⁴ and got quite different results (by 725 kcal per day, an imbalance which would hypothetically lead to 35 kg (!) of weight gain or loss after a year):

On the other side of the “energy balance” equation is your personal energy intake. Here are some comparisons, which most of us probably would have gotten wrong:

In conclusion, while you cannot gain weight without overeating, “having a negative energy balance” is not a practical advice for patients. Energy intake and expenditure estimates are both way too rough to be useful.

How to lose weight, according to the evidence?

Are weight loss interventions in primary care effective? Yes, if you are satisfied with short-term results. A recent BMJ review (2022)¹⁷ included 34 trials in primary care with quite intensive interventions (each patient received a median of 12 lifestyle sessions). After one year, patients lost on average 2.3 kg, after two years a loss of 1.8 kg remained. Longer follow-up was not reported. But, as weight regain is common, what about studies on long-term maintenance? My review of the literature identified only three (!) studies with at least three-years of follow-up. If you know of another such study, please just contact me (no one did in the ten years I teach this topic). Here they are in one graph:

While these studies showed meaningful effects after one year, the weight loss after five years (2-5 kg) is modest only. Some consider these long-term effects to be clinically significant, others don’t. Nevertheless, keep in mind that these small effects were caused by highly intensive and continuous lifestyle interventions (>120 lifestyle sessions each in the Lancet study and the Obesity study), which patients usually cannot receive in real life.

However, you probably know a patient who maintained long-term weight loss. Yes, for some individuals it’s possible. The Obesity 2014 study¹⁸ showed that of those who lost ≥10% of their weight at year one, almost 40% were able to keep their weight loss of around 15% at year eight. But others even gained weight. On average, participants lost less than 5 kg.

=> If intensive weight loss interventions were a drug, they probably wouldn’t receive FDA/EMA approval (due to lack of clinically significant long-term effectiveness).

Why is long-term weight loss so difficult to achieve? One reason is hormonal regulation. One year after a weight loss, leptin, peptide YY, cholecystokinin, insulin, ghrelin, gastric inhibitory polypeptide, and pancreatic polypeptide levels are still significantly changed, which leads to increased feelings of hunger and therefore weight regain. In other words, our body strongly regulates itself to reach its target weight.¹⁹ Other reasons are that willpower is simply limited (especially in the long-term) and that genes, gut microbes, and the obesogenic environment – which all contributed to the development of obesity initially – stay unchanged and still exert their influence.

What do Guidelines on Obesity Management recommend?

A few years ago, I performed a systematic review on such evidence-based guidelines¹ to answer this question. Interestingly, we found considerable agreement on how to manage overweight and obesity in primary care. Patients should join a multidisciplinary lifestyle program which includes eating less, exercising more, and changing behaviors. Pharmacological measures were recommended only additionally to a lifestyle program and bariatric surgery only if all non-surgical interventions have failed. While I am grateful to the experts who developed these comprehensive guidelines, I am skeptical it works in the long-term. Also, I believe that there is a much better approach than “eating less, exercising more” (see “conclusion” below).

What about the new weight loss drugs, GLP-1 analogs?

There is much to say! I therefore wrote a blog article about it which you can find here: Key Facts GPs Should Know About GLP-1 Analogs.