Optimal rate of weight loss:
The author recalled an article by calorie restriction and nutritional ageing experts Dr Michael Rae PhD and his ex-wife:
““You’re losing weight too fast,” she says, with the crisp authority of a doctor handing me some bad but easily remedied news. “You’ve lost twenty pounds in two months, and you probably shouldn’t lose more than five pounds a month. You need to start eating more.” This appears to be a cue for the evening’s two alpha geeks—Paul and Michael—to launch into dueling mini-lectures on the dire biophysics of rapid weight loss. “When you do CR, you’re not just losing fat,” Michael explains. “You’re losing muscle; you’re losing bone.” Shed weight too fast, and you can even shrink the most important muscle you have, your heart, running the same risk of cardiac arrest that makes anorexia such a dangerous obsession. “Yeah, sure, all that,” Paul jumps in, “but the real thing is your immune system.” Paul seems rather fonder of arcane medical jargon than Michael, and I’m not sure I follow why it’s my white blood cells I really need to worry about, but I’m not inclined to doubt him on it. This is a man, after all, who haunts his local medical lab the way some men haunt casinos, hewing to a schedule of testing so meticulous that one out-of-state lab has come to rely on Paul’s results to calibrate its own blood-testing equipment.” (Dibbell, 2007)
Too fast weight loss = > 2 kg per month (= 5 lbs / month, as quoted above)
This was backed up by a randomised primary study (Garthe, Raastad, Refsnes, Koivisto, & Sundgot-Borgen, 2011) that showed that in body fat 7-27% (95% CI) athletes, BMI 24.9 average (author estimated), 0.5 kg/week weight loss (2kg per month) resulted in a 1.3% to 2.9% increase in skeletal muscle mass, whilst it resulted in a -1.6% loss to 1.2% increase in skeletal muscle mass in those that lost 1 kg/weight per week.
Scoping potential harms of weight loss (and particularly rapid weight loss)
As based on the above article these were determined to include:
- Skeletal muscle loss
- Bone loss
- Cardiac muscle loss
- Decreased immunity (immunocompromise)
References were then sought to back up this expert opinion
1. Skeletal muscle loss
Search sensitivity: 99%, specificity: 70% versus hand searching (Wilczynski, McKibbon, & Haynes, 2011)
systematic[sb] AND (weight loss muscle loss)
systematic[sb] AND (("weight loss"[MeSH Terms] OR ("weight"[All Fields] AND "loss"[All Fields]) OR "weight loss"[All Fields]) AND ("muscles"[MeSH Terms] OR "muscles"[All Fields] OR "muscle"[All Fields]) AND loss[All Fields])
- No systematic reviews identified so proceeded to search for non-systematic reviews
“weight loss muscle loss”
("weight loss"[MeSH Terms] OR ("weight"[All Fields] AND "loss"[All Fields]) OR "weight loss"[All Fields]) AND ("muscles"[MeSH Terms] OR "muscles"[All Fields] OR "muscle"[All Fields]) AND loss[All Fields]
Sort Filter: Best Match
In persons with normal weight, the contribution of fat-free mass loss often exceeds 35% of total weight loss (47, 48), and weight regain promotes relatively more fat gain (49). In persons who are overweight or obese, fat-free mass contributes only ∼20–30% to total weight loss (48, 50–59), and weight regain does not prevent fat-free mass regain (49). (Cava, Yeat, & Mittendorfer, 2017)
On analyzing the literature on resistance or endurance type exercise to reduce the amount of muscle loss during weight loss in obese individuals, i.e. to shift towards ‘fat burning’, (Cava et al., 2017) concluded that “Together, these results suggest that resistance-type exercise is an effective strategy to attenuate or even prevent the weight-loss–induced loss of muscle mass during weight loss, whereas the effects of endurance-type exercise on muscle mass during weight loss are uncertain.”
Assuming this extends to normal BMI persons, weight loss induced skeletal muscle loss can be reduced primarily by regular weekly resistance exercise, and potentially less so by endurance exercise.
Evidence was then found in normal BMI persons (author estimated BMI of 24.9, and of body fat % 17% (7% to 27%) that
2. Bone loss
Search sensitivity: 99%, specificity: 70% versus hand searching (Wilczynski et al., 2011)
systematic[sb] AND (weight loss bone loss)
systematic[sb] AND (("weight loss"[MeSH Terms] OR ("weight"[All Fields] AND "loss"[All Fields]) OR "weight loss"[All Fields]) AND ("bone diseases, metabolic"[MeSH Terms] OR ("bone"[All Fields] AND "diseases"[All Fields] AND "metabolic"[All Fields]) OR "metabolic bone diseases"[All Fields] OR ("bone"[All Fields] AND "loss"[All Fields]) OR "bone loss"[All Fields]))
The apriori selected subgroup analysis in a meta analysis of changes in bone mineral density with weight loss showed there was bone mineral density loss in calorie restricted diets however the I^2 was over 85% in all these subgroups suggesting this conclusion is potentially invalid. However, for subgroups of each of total and spine (lumbar) bone mineral density, exercise programs, with or without calorie restriction prevented loss of bone mineral density and had an I^2 at most of 50.8%. However, the I^2 for spinal density was over 80%. This suggests that bone mineral density losses may be prevented at least on total body measures and hip measures, by ensuring exercise is done concurrently with the weight loss program. (Soltani, Hunter, Kazemi, & Shab-Bidar, 2016)
3, Cardiac muscle loss
No results were found for weight loss cardiac output or weight loss cardiac mass on clinical queries search; this was due to poor MeSH mapping of “mass” to molecular mass
However, a search in standard pubmed search bar of “weight loss cardiac mass” yielded some relevant results, with the MeSH of ventricular remodeling (as assessed my MRI ideally) being understood
Standard pubmed search of “weight loss ventricular remodeling” yielded further results with both terms MeSH mapping
Finally, as it was not clear if low ventricular mass was dangerous, standard search of “low left ventricular mass” was done
It was found that there was a linear dose response between weight loss and left ventricular mass regression, suggesting that this relationship is true. This relationship was independent of BMI, and whilst the study was based on BMIs of 23.8 to 31.5, as of this independence this could be extrapolated beyond this BMI range (Soltani et al., 2016).
The author understood that high ventricular masses was associated with poor outcomes, as confirmed by a review paper uncovered: “Much of the adverse effects of obesity may be mediated through adverse effects on cardiac structure and function. Decades of research3–5 have established that increased left ventricular (LV) mass (weight), even below levels exceeding reference values which demarcate hypertrophy, and alterations of the geometry of the LV are associated with adverse cardiovascular outcomes, including diastolic dysfunction and heart failure—often with preserved ejection fraction.” As quoted from (Gottdiener & Kop, 2017).
However, the author was not clear on potential dangers of low ventricular mass that could be induced by rapid or significant weight loss. Anorexia nervosa patients with mean BMI of 15.5 were found to have low left ventricular mass, but it is not clear whether this is a contributor to the high mortality in anorexia. There was a strong R=0.74 correlation with left ventricular mass and BMI in this study. (Kuwabara, Niwa, Yamada, & Ohta, 2018)
In a systematic review of anorexia low cardiac mass was observed and cardiac risks as a cause of mortality: “This review demonstrated that the most common cardiac abnormalities in AN are bradycardia and QT interval prolongation, which may occasionally degenerate into ventricular arrhythmias such as Torsades des Pointes or ventricular fibrillation. As these arrhythmias may be the substrate of sudden cardiac death (SCD), they require cardiac monitoring in hospital. In addition, reduced cardiac mass, with smaller volumes and decreased cardiac output, may be found.” (Giovinazzo et al., 2018)
Theoretically, cardiovascular exercise should reduce the loss of cardiac mass and cardiac output that occurs during weight loss. However, no references could be found for this.
4. Decreased immunity
systematic[sb] AND (weight loss immune (or immunity/infection separate search) yielded no results
standard search of weight loss immune, weight loss immunity, weight loss infection, weight loss respiratory tract infection yielded no results
No clinical outcomes results could be found for weight loss and immunity related outcomes.