We are not aware of it, but our eating habits are pretty unnatural. We eat from the moment we wake up to when we fall asleep again. If we can break this pattern and start doing intermittent fasting, we can make dramatic changes to our body. We lose fat, get fitter and build up extra muscle mass researchers at the Salk Institute for Biological Studies in the US believe. They investigated the effects of intermittent fasting in a series of animal studies.
The researchers gave mice standard food which would enable them to live healthily to a ripe age [N], food that consisted for 60 percent of fat [F], or food that consisted for 30 percent of fat and 25 percent of sugar [FS]. If you give mice food that contains extra fat or sugar then they eat more of it and they put on weight and become more unhealthy.
For one period of several months the mice were allowed to eat whenever they wanted [A], on another occasion they were only given access to food during an 8-9 hour period per 24 hours. Interestingly, during that shorter period of time the animals ate almost as much as they did when they were given unrestricted access to food.
The figures below show the body composition and fat percentage of different groups of mice. Whether the animals were on a healthy diet or a high-fat one, when they did intermittent fasting they lost weight.
FAA = six months unlimited access to high-fat food;
FTT = six months access to high-fat food for 8-9 hours a day;
FTA = first three months access to high-fat food for 8-9 hours a day, then three months unlimited access to high-fat food;
FAT = first three months unlimited access to high-fat food, then three months access to high-fat food for 8-9 hours a day;
NAA = six months unlimited access to high-fat food;
NTT = six months access to normal food for 8-9 hours a day;
NTA = first three months access to normal food for 8-9 hours a day, then three months unlimited access to normal food;
NAT = first three months unlimited access to normal food, then three months access to normal food for 8-9 hours a day.
In the mice that were given normal food, intermittent fasting had a positive effect on lean mass.
The researchers got the mice to run on a treadmill to the point of exhaustion. This was done after the mice had been exposed to different eating regimes for a period of 12 weeks.
NA = unlimited access to normal food;
FA = unlimited access to high-fat food;
9hFT = access to high-fat food for 9 hours a day;
12hFT = access to high-fat food for 12 hours a day;
5T2A = access to high-fat food for 9 hours on weekdays, unlimited access to high-fat food at weekends;
FSA = unlimited access to high-fat (40 percent) and high-sugar (25 percent) food;
FST = access to high-fat (40 percent) and high-sugar (25 percent) food for 9 hours a day.
As you can see, intermittent fasting for 16 hours a day improved endurance capacity. Intermittent fasting for 12 hours had little effect. Intermittent fasting made mice with an unhealthy diet even fitter than mice that had unlimited access to healthy food. (The researchers did not look at the effect of intermittent fasting on mice that ate a standard diet.)
Intermittent fasting made the animals more sensitive to insulin, reduced the synthesis of inflammatory proteins such as TNF-alpha and interleukin 1-beta, and boosted the activity of enzymes involved in fat burning in the animals’ cells.
“Our results highlight the great potential for time restricted feeding in counteracting human obesity and its associated metabolic disorders”, the researchers wrote. “Future work should explore the role of known metabolic and circadian regulators in restoring the organism’s energetics to normalcy under time restricted feeding.”
“Furthermore, it is worth investigating whether the physiological observations found in mice apply to humans. A large-scale randomized control trial investigating the role of time restricted feeding would show whether it is applicable to humans.”
Time-restricted feeding is a preventative and therapeutic intervention against diverse nutritional challenges.
Because current therapeutics for obesity are limited and only offer modest improvements, novel interventions are needed. Preventing obesity with time-restricted feeding (TRF; 8-9 hr food access in the active phase) is promising, yet its therapeutic applicability against preexisting obesity, diverse dietary conditions, and less stringent eating patterns is unknown. Here we tested TRF in mice under diverse nutritional challenges. We show that TRF attenuated metabolic diseases arising from a variety of obesogenic diets, and that benefits were proportional to the fasting duration. Furthermore, protective effects were maintained even when TRF was temporarily interrupted by ad libitum access to food during weekends, a regimen particularly relevant to human lifestyle. Finally, TRF stabilized and reversed the progression of metabolic diseases in mice with preexisting obesity and type II diabetes. We establish clinically relevant parameters of TRF for preventing and treating obesity and metabolic disorders, including type II diabetes, hepatic steatosis, and hypercholesterolemia.
PMID: 25470547 PMCID: PMC4255155 DOI: 10.1016/j.cmet.2014.11.001 [PubMed – indexed for MEDLINE]