This, according to a study by Ruth Brown and colleagues from Toronto’s York University, published in Medicine and Science in Sports and Exercise.
The study included 58 adult men and women of either normal weight (NW) or overweight (OW), who reported either attempting (WL) or not attempting weight loss (noWL)
Following 25 mins of exercise on a treadmill at either a moderate (60% HRmax) or a vigorous intensity (75% HRmax), participants were asked to estimated the number of calories they expended through exercise and create a meal that they believed to be calorically equivalent to the amount of calories they had just burnt.
Both the moderate and intense exercise groups were on average spectacularly wrong in their estimates.
In contrast, the active weight loss (WL) groups appeared to do far better at estimating energy consumption than the non-WL groups.
As an example, following vigorous exercise, the OW-noWL overestimated energy expenditure by 72%, and overestimated the calories in their food by 37%.
Although the WL groups did better, all groups showed a wide range of over and underestimation (-280 kcal to +702 kcal).
These findings show that while most people tend to over or underestimate caloric expenditure with exercise, overweight adults who are not attempting weight loss may be even more off the mark than others.
The most obvious solution would be to use some kind of monitor that does a better job of predicting calories consumed that just guessing.
That is of course, if overcompensating is not your goal (as in people who actually gain weight when they begin exercising).
For those interested in staying in energy balance, perhaps simply stepping on the scale regularly during the week should be enough.
For those interested in losing weight, they may need to be reminded that exercise (alone) is actually a pretty inefficient way to lose weight, so the calories burnt during exercise probably don’t matter all that much for weight management (despite all other benefits of exercise – its the calories you eat or drink that count).
Now Suzanne Higgs and Jason Thomas from the University of Birmingham, UK, in a paper published in Current Opinion in Behavioral Science review the role of social norms in eating behaviours and discuss how these norms could potentially be targeted to improve eating behaviours.
“We eat differently when we are with other people compared with when we eat alone. Our dietary choices also tend to converge with those of our close social connections. One reason for this is that conforming to the behaviour of others is adaptive and we find it rewarding. Norms of appropriate eating are set by the behaviour of other people, but also shared cultural expectations and environmental cues. We are more likely to follow an eating norm if it is perceived to be relevant based on social comparison. Relevant norms are set by similar others and those with whom we identify… Norm matching involves processes such as synchronisation of eating actions, consumption monitoring and altered food preferences.”
“Social norms may have had a role to play in recent rises in obesity by reinforcing new behaviour patterns associated with overeating and weight gain. For example, increases in average portion size may have created new consumption norms that are diffused through social networks. It might also be that the social context of eating has changed recently in ways that favour overconsumption. For example, more people eating away from home in fast food restaurants with others might be associated with social facilitation of eating.”
If, how and to what extent, eating culture can be changed at a population level through public health and policy interventions will certainly remain the subject of further study.
Now a study by Robert Eckel and colleagues, published in Current Biology, illustrates how sleep deprivation and timing of meals can markedly alter insulin sensitivity.
Studies were conducted in 16 healthy young adults (8w) with normal BMI. Following a week of 9-hr-per-night sleep schedules, subjects were studied in a crossover counterbalanced design with 9-hr-per-night adequate sleep (9-hr) and 5-hr-per-night short sleep duration (5-hr) conditions lasting 5 days each, to simulate a 5-day work week. Sleep was restricted by delaying bedtime and advancing wake time by 2 hr each.
Energy balanced diets continued during baseline, whereas food intake was ad libitum during scheduled wakefulness of 5- and 9-hr conditions.
Overall, the simulated 5-day work week of 5-hr-per-night sleep together with an ad libitum diet resulted in a 20% decrease in oral and intravenous insulin sensitivity, which was compensated for by increased insulin secretion..
These changes persisted for up to 5 days after restoring 9-hr sleep opportunities.
The authors also showed that shifting circadian rhythm resulted in morning wakefulness and eating during the biological night, a factor that may promote weight gain over time.
Yesterday, I posted about the interesting study by Madjd and colleagues suggesting that drinking water may be better for weight loss than drinking diet beverages.
But what exactly is the evidence that low-calorie sweeteners (of which there are many) may actually have non-caloric effects on energy intake or body weight?
The authors assessed both animal and human studies involving the consumption of low-calorie sweeteners in conjunction with an ad libitum diet.
In 62 of 90 animal studies exposure to low-calorie sweeteners did not affect or decreased body weight. Of 28 studies that did report increased body weight, 19 compared compared low-calorie sweeteners with glucose exposure using a specific ‘learning’ paradigm.
In humans, 12 prospective cohort studies found inconsistent associations between the use of low-energy sweeteners and body mass index, with overall minimal effects at best.
A meta-analysis of short-term randomized controlled trials (involving 129 comparisons) showed reduced total energy intake for low-calorie sweetener versus sugar-sweetened food or beverage consumption before an ad libitum meal (about −94 kcal per day), with no difference versus water (−2 kcal per day).
These findings were consistent with energy intake observations in sustained intervention randomized controlled trials (10 comparisons), a meta-analysis of which (with study durations ranging from 4 weeks to 40 months) showed that consumption of low-calorie sweeteners versus sugar led to relatively reduced body weight (nine comparisons), and a similar relative reduction in body weight compared to water (three comparisons).
Thus, contrary to what is often stated in popular media or even by some experts, there is little if any evidence either from animal or human studies that the use low-caloric sweeteners has any measurable impact on energy intake (other than reducing total caloric intake) or body weight.
Thus, the authors conclude that
“Overall, the balance of evidence indicates that use of low-energy sweeteners in place of sugar, in children and adults, leads to reduced energy intake and body weight, and possibly also when compared with water.”
Obviously, even this analysis is not going to silence the sceptics, who will continue to claim that somehow low-calorie sweeteners are still messing up your energy intake or metabolism.
However, it may be fair to conclude that if indeed such effects exist, their magnitude is likely marginally and of doubtful clinical significance.
I will continue recommending that my patients do their best to replace sugar with non-caloric sweeteners if giving up their liking for sweet foods or beverages is not an option.
According to conventional wisdom, beverages with artificial sweeteners should be weight neutral, given that they do not contain calories. However, whether this is true or not remains controversial. Besides the epidemiological evidence suggesting that the consumption of artificially sweetened beverages may be associated with higher body weights, there are also a range of physiological studies suggesting that artificial sweeteners can induce metabolic changes (including changes in taste preferences) that may promote weight gain.
Now, a study by Ameneh Madjd and colleagues from the University of Nottingham, UK, and the Tehran University of Medical Sciences, Iran (where the study was conducted) published in the American Journal of Clinical Nutrition, suggests that replacing ‘diet beverages’ (DBs) with water may not only result in greater weight loss but may also have greater benefits in terms of glucose metabolism.
The study was conduced in 89 women with overweight or obesity who usually consumed DBs in their diet.
Participants were randomized to either replace their DBs with water or continue drinking DBs 5 times/wk after their lunch for 24 wk (DB group) while on a 24-week weight-loss program.
71% of participants completed the trial (32 in the DB group, 30 in the water group).
Over the 24 weeks, the water group lost about 1.2 Kg more than the DB group (mean weight loss of both groups was about 8 Kg).
Improvements in fasting insulin levels, HOMA index and 2-hr post-prandial glucose also tended to be greater in the water than in the DB group.
Thus, the authors conclude that replacement of DBs with water after the main meal may lead to greater weight reduction and more favourable metabolic benefits during a weight-loss program.
As for the possible mechanisms that would account for these findings, the authors speculate based largely on self-reported changes in food intake that the water-drinking group may have been more compliant to the recommended diet and may have marginally reduced their carb intake. There is also the possibility that drinking water (rather than DBs) may support weight loss through other mechanisms.
Overall, I am not sure what to really make of this study. Clearly, being able to replace DBs with water may be beneficial. On the other hand, the more common problem in my practice is dealing with patients who consume larger amounts of sugar-sweetened beverages (SSBs rather than DBs) and I would imagine that if a shift to water is too drastic, DBs may at least be substantially better than continuing on with SSBs for these patients.