Combining 16:8 Time-restricted Eating and Strength Training Improves Cardiometabolic Health, Body Composition, and Strength
A 1-year intervention of TRE and resistance training produced superior benefits for several health parameters compared to a "normal diet" without compromising strength gains.
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As the popularity of intermittent fasting (IF) grows, so does the research to support its beneficial effects for improving on a wide variety of health outcomes including blood glucose regulation, body composition, age-related functional decline, and maybe even cancer risk.
It is important to note that intermittent fasting is not a panacea, and there are plenty of healthy ways to eat that do not involve intermittent fasting. However, intermittent fasting seems to be a sustainable lifestyle modification for many people who find major benefits using a daily form of IF known as time-restricted eating (TRE) — which involves consuming all of one’s calories in a predetermined “eating window” during the day, and then fasting for an extended period from late-afternoon until around lunch the next day. One of the most popular forms of TRE is 16:8 — where one fasts for 16 hours and then eats within an 8-hour time window during the day.
Just as there is no ideal length of IF, there is nothing magical about a 16:8 fast, but it tends to be very doable and also allow for enough fasting time to exert some benefits. Whether or not this type of fasting could have long-term benefits if adhered to for years is relatively unknown, as most studies to date have been short-term (i.e. 8-12 weeks) in duration.
As a lot of individuals participating in TRE are also engaging in some type of aerobic, resistance, or combined training program, it is of a general interest to know how TRE might affect training adaptations or “gains.” Some claim that extended fasting might hamper strength training improvements, and this information is relevant for those looking to build muscle/strength while also engaging in TRE.
A new study published in Medicine and Science in Sports and Exercise (MSSE) was one of the first to investigate the effects of extended (12 months) TRE in healthy participants who were also experienced in resistance training. They looked at how extended TRE affected a slew of cardiometabolic biomarkers as well as resistance training performance including muscle mass and strength.
Brief study methods
20 participants (all males) around 30 years of age on average participated in this study. As mentioned above, all participants reported at least 5 years of resistance training experience.
Participants were split into 2 groups of 10 and randomly assigned to either a TRE condition or a normal diet (ND condition), which included the following eating patterns:
- TRE: 8-hour daily feeding window with 3 meals consumed at 1pm, 4pm, and 8pm
- ND: 12-hour daily feeding window with 3 meals consumed at 8am, 4pm, and 8pm
These diets were adhered to for 12 months, during which all participants completed ~3 strength training sessions per week (unsupervised).
Study measures were taken at baseline, 2 months, and 12 months. Blood markers included glucose and insulin, inflammatory cytokines, cholesterol and triglycerides, insulin-like growth factor (IGF-1), thyroid hormones, testosterone, and leptin and adiponectin. Body composition, resting energy expenditure and respiratory exchange ratio, 1-repetition max for leg press and bench press, and muscle size (cross-sectional area) were also assessed at all time points.
Something that happens (unfortunately) in a lot of IF/TRE studies is that the fasting group naturally reduces their overall calorie intake despite no instructions to do so. This is an inherent limitation, because it prevents us from separating the independent benefits of fasting from those of calorie restriction. In this particular study, participants in the TRE group ate about ~180 calories less per day compared to baseline, while the normal diet group kept their intake similar. While 200 calories per day may not seem significant, it’s about a ~10% reduction and is likely a physiologically meaningful reduction. On top of that, the TRE group also reduced the percent of calories that came from carbohydrates and fat, which can be seen in the table below.
- Glucose and insulin levels were reduced at 2 months (by ~9% and 28%, respectively) and 12 months (by ~9% and 31%) in the TRE group but were unchanged in the ND group
- TRE reduced testosterone by 3% at 2 months and ~16% at 12 months
- TRE reduced IGF-1 levels by ~14% at 2 and 12 months
- HDL cholesterol was improved at 2 and 12 months and LDL cholesterol was reduced at 12 months in the TRE group
- Triglycerides were reduced in the TRE group at 2 and 12 months
- Inflammatory cytokines including IL-6, IL-1𝛽, and TNF-ɑ were reduced at 12 months in the TRE group (IL-6 was also reduced at 2 months)
Body composition and muscle size
- TRE reduced body mass and fat mass after 12 months
- TRE also reduced levels of visceral adipose tissue (organ fat) at 12 months by ~18%
- The ND group increased fat-free mass by 3% at 12 months
- TRE decreased the cross-sectional area of the arm and thigh muscle, while the ND increased arm and thigh muscle cross-sectional area
- TRE increased maximum strength on leg press (~15%) and bench press (~15%)
- ND increased maximum strength on leg press (~14%) and bench press (~10%)
Resting energy expenditure and RER
- TRE decreased resting energy expenditure, while no change was observed in the ND group
- TRE promoted an increase in fat metabolism at rest, as shown by a reduction in RER
Thoughts and musings
For cardiometabolic health and metabolism, this study would suggest that a shorter feeding window is superior. Several markers of glucose control, blood lipids, and inflammation were all improved during the 12-month TRE but were not observed in a group eating a “normal diet” with a 12-hour feeding window. This comes with the obvious caveat that the TRE group reduced their calorie intake, but results are interesting nonetheless.
However, there were several outcomes for which TRE seems to be suboptimal, at least for those looking to maximize resistance training outcomes. This includes reductions in anabolic hormones including testosterone and IGF-1, along with a failure to increase fat-free mass despite increases in strength. Granted, the TRE group did lose fat mass and thus improve their body composition. However, if muscle gain and hypertrophy are the primary goals, shortening one’s feeding window to 8 hours may not be the most optimal choice.
That anti-inflammatory effects and reductions in cardiometabolic risk factors were observed in healthy, young individuals participating in TRE is quite promising, since we might expect even greater improvements in “at risk” individuals or those with larger health improvements to make. I think that is the draw of TRE — it can be utilized by anyone and customized to fit one’s personal preferences and health goals.
With that being said, even though the 16:8 protocol is highly popular, everyone might find a different length or variation of TRE to be more suitable. Whether you choose to alter the duration of the fast OR at what time of day the fast occurs (i.e. early or late TRE), there are likely health benefits to be had from consistent TRE. It’s an easily implementable lifestyle intervention. Like all things in life, timing is everything.
Thanks for reading. See you next Friday.
Moro T, Tinsley G, Pacelli FQ, Marcolin G, Bianco A, Paoli A. Twelve months of time-restricted eating and resistance training improve inflammatory markers and cardiometabolic risk factors. Medicine & Science in Sports & Exercise. 2021;Publish Ahead of Print.