Science Recap: Fructose, Fitbits, Antibiotics and the Microbiota, and More
Here is a recap of some of the most interesting science and health information from the past few weeks.
This week, we learned from Dr. Arya Sharma about a recent study suggesting that Fitbit may indeed be useful for enhancing physical activity. Dr. Sharma also highlighted research showing that sleep loss and circadian misalignment can have a significant detrimental impact on insulin sensitivity.
Next we turn to Dr. Adel Moussa of Suppversity, who showed that artificial sweeteners might cause rodents to put on weight – though this study arguably raises more questions than it answers. In a separate post, Moussa also reveals how fructose, surprisingly, might actually help you keep your post-workout appetite under control.
Finally, Aeon published a fascinating video in which Dr. Martin Blaser explains vividly why microbial diversity in the human gut is crucial to our health – and how abuse of antibiotics may be silently decimating that ecosystem.
Better Aging Series Recap
So far in my series on aging, I have written on the problems and opportunities of aging, calorie restriction, protein restriction, and fasting, and also of the perils and opportunities with smoking and alcohol consumption. More articles are coming your way, but here are the current ones to date:
- Article 1: Age Better Today. Is This Really Possible?
- Article 2: Slowing Down Aging with Dietary Restrictions
- Article 3: Does Protein Restriction and Fasting Slow the Aging Process?
- Article 4: How Much Alcohol Should I Drink to Age Better?
Fitbit Can Inspire People to Move – and Stick with It
Despite the growing popularity of such devices, there have been relatively few studies out there that have employed the activity tracker Fitbit as an intervention to increase physical activity. Recently however Lisa Cadmus-Bertram and colleagues published a randomized controlled intervention trial with 25 overweight or obese women using the wearables. Participants were advised to use Fitbit for a 16 week period.
Historically, studies using such devices have shown a dramatic drop in use over time. This makes it hard to tell whether using activity monitors is particularly useful. However, for this study, overall engagement appeared to be strong: participants logged on average 10 hours or more/day of Fitbit wear on 95% of the 112 intervention days. And adherence did not decline much over time (only 8% for steps and 14% for moderate-to-vigorous physical activity by 16 weeks).
Dr. Sharma points out that these 25 participants may not necessarily be representative of the general population. It is a relatively small sample of obese women, who may have had extraordinary short-term motivation to change their activity levels. Nevertheless, the study appears to validate the use of digital wearables to monitor activity levels and motivate lifestyle change.
Sleep Deprivation and Distorted Sleep Timing Contribute to Insulin Resistance
Over the last 10-15 years, research has revealed sleep and circadian rhythms as important variables in appetite and energy balance. In a new study published in Current Biology, Robert Eckel and colleagues investigated how sleep deprivation, as well as altered sleep timing, can affect insulin sensitivity.
The researchers recruited 16 healthy young adults with normal BMI. After a week of 9-hour-per-night sleep schedules, subjects were exposed to either adequate sleep (9 hours time in bed per night) or short sleep (5 hours time in bed per night) conditions. Each condition lasted for 5 days. The sleep-restricted condition was achieved by delaying bedtime and advancing wake time by 2 hours. This results in a double whammy of reduced sleep and altered sleep timing – both can independently influence metabolic functioning.
The study found that short sleep reduced insulin sensitivity by 20%. This also resulted in increased insulin secretion to compensate for the reduced insulin sensitivity. This metabolic derangement continued for up to five days after returning to adequate sleep conditions.
The study lends support to the preponderance of the evidence which suggests that sleep restriction and circadian misalignment may lead to weight gain, as well as greater risk of developing diabetes. These findings are certainly relevant to shift workers – and to everyone else who struggles to get enough sleep, or with consistent sleep timing.
Adding Artificial Sweeteners May Cause Rodents to Gain Weight – Independent of How Much Food They Eat
Some epidemiological evidence has associated artificial sweeteners with weight gain and metabolic dysfunction. However, mechanisms for this link have not yet been clarified. In fact, controlled human trials show that consumption of artificial sweeteners can actually aid in fat loss. Results have been mixed in animal trials.
In a recent study, Kelly Carraro Foletto and colleagues randomly assigned 16 rats to receive about 80 calories of either saccharin-sweetened yogurt or unsweetened yogurt. This was in addition to their normal food and water, to which they had free access. They measured the total food intake and weight gain on a weekly basis over the duration of the study. The investigators also measured fasting leptin, glucose, insulin, peptide YY, and insulin resistance (via homeostatic model assessment, or HOMA-IR), to determine whether changes in body mass could be attributed to shifts in key hormones associated with appetite and blood sugar regulation.
Rodents receiving saccharin-sweetened yogurt experienced a 5% increase in weight gain over fourteen weeks. Strangely, the researchers did not report differences in insulin resistance, fasting leptin, or peptide YY levels – all of which would be expected to change in response to a pathological elevation in fat mass. They also did not measure the body composition of the subjects to determine what type of mass was gained.
Why did the rodents consuming the saccharin-sweetened yogurt put on extra weight? It’s unclear. Foletto et al attribute their findings to several potential mechanisms. They suggest it may be due to changes in glucose transport, mediated by sweet taste receptors in the gut. Or, it may be caused by shifts in energy expenditure associated with saccharin.
Nevertheless, recent human clinical trials still appear to support artificial sweeteners for weight loss. It remains to be seen whether these intriguing rodent studies are applicable to humans – and whether they are strong enough evidence to dissuade us from using such sweeteners.
A Breakfast Higher in Fructose May Help Keep Post-Cardio Hunger under Control
Hong Kong researchers compared effects of three breakfasts with identical amounts of calories and carbohydrates on appetite scores in ten healthy young males. The meals differed only in glycemic index, and in the amount of fructose. The participants rated different aspects of their own appetites at thirty-minute intervals during the 2-hour window after they ate the breakfasts. Two hours after eating, subjects engaged in one hour of brisk walking. They then rated their appetite during the one-hour recovery period following the walking bout.
In the first two-hour period following the three different meals, the participants’ appetites were similar. However, after the walk, the high fructose meal stood out for its apparent ability to keep post-workout munchies at bay. This suggests a (seemingly) novel effect of fructose. Moussa points out that it might have been more interesting if the study had been able to test whether the subjective reduction in appetite also translated to a reduction in food intake on the part of the subjects.
Why the high-fructose meal would influence appetite in this way remains unclear. It has been argued in the past that fructose is more satiating because of its lower glycemic index, and accordingly its lesser propensity to cause spikes in insulin. However, this study found that neither insulin nor glucose excursions were significantly different after the different meals. So what could be causing it? Moussa speculates that it may be due to changes that weren’t assessed in this study – possibly in gut hormones that affect our appetite and sense of fullness. One would hope that future studies investigating this phenomenon might measure such variables.
Past studies have shown that isolated consumption of high amounts of free fructose is detrimental to appetite control. But research like this suggests that avoiding fructose may not be optimal. Like all things in nutrition, the dose makes the poison. If you find that low-intensity cardio triggers your appetite, you might try switching up your pre-workout meal to contain more fructose to see if that helps. Comment below if you feel it helps or doesn’t.
Antibiotics Make Our Guts Less Diverse
In this short film, Dr. Martin Blaser explains the historically underappreciated impact of antibiotic use on the diversity of microbial species populating the human gastrointestinal system. Every single time someone undergoes a round of antibiotics, a few strains of bacteria native to that person’s gut are rendered extinct. A recent study suggested that of us may have already lost as much as half of our diversity.
Why does diversity matter? Many bacterial strains in the body appear to function as regulators to the immune system. Blaser hypothesizes accordingly that loss of microbial diversity may be fueling the modern proliferation of allergies and autoimmune diseases.
This brings to mind an article in Mother Jones from a couple of years ago, which pointed out the curious correlation of antibiotic prescription rates and obesity rates in certain US states. These two graphs starkly illustrate this association.
While it would be inappropriate to assume from this that overuse of antibiotics are directly responsible for the obesity epidemic, it seems increasingly plausible that they are a contributing factor.