Does Intermittent Fasting Work?

The research is pretty clear that IF can help people lose weight. That said, in all of the available research, IF is only effective with weight loss when the subjects are in a caloric deficit. This is a common theme across all diets: If the dietary approach enables you to maintain a consistent caloric deficit, weight loss will be achieved; if not, weight loss will not occur. Ultimately, a sustained caloric deficit is the only way to achieve weight loss: It bears repeating that IF is not a panacea.

In my personal practice, it has become increasingly common for people following an IF protocol to reach out to me frustrated with their inability to lose weight. In every case these people have self-selected the late-eating style of IF, along with the habit of overindulging at dinner or later, thus negating the caloric deficit they created when they skipped their morning meal.

Further to this anecdote, research shows us that people who eat after dinner blunt fat-burning during sleep, leading to less body fat burned overall. This same reduction in fat-burning does not occur with meals consumed during the day (like breakfast), and a 2013 study showed that those who eat a large breakfast relative to those who eat a large dinner actually lose more weight overall- even when calories are equal. How is this possible you ask? The answer would seem to be the result of circadian rhythms and subsequent hormone cascades.

Circadian rhythms are 24-hour cycles that dictate the physiological processes of living creatures (in this case, humans). These rhythms are influenced by external factors such as light, food intake, and physical activity. The human body has one main circadian clock (the suprachiasmatic nucleus, or SCN), although nearly every cell in the body has its own peripheral clock. Exposure to light serves as the main control for the SCN, while food intake has a major impact on peripheral clocks.

Quite simply, humans evolved with the rising and setting of the sun, and our clocks and healthy physiology are tied to this pattern. Have you ever experienced jet lag? This is because you tampered with your internal clocks in a pronounced way; jet lag is the most relatable way to feel the negative health impacts of going against circadian rhythms.

Shift work also breaks circadian rhythms and shift workers have a significantly higher risk of developing type-2 diabetes. Further to that, a 10-day human lab study showed that breaking circadian rhythms can induce blood glucose responses in the range typical of a pre-diabetic state (yes, in just 10 days). The aforementioned 2013 study also found that a big breakfast and small dinner (relative to a small breakfast and big dinner), led to improved blood markers; while both groups in this study lost weight due to a caloric deficit, the baseline health between the groups was markedly different and was attributed solely to a difference in meal timing.

By nature, humans are intended to see light early in the day and to consume food during daylight hours (and more favourably in the morning hours), which segues us nicely into our final question:

Any question regarding health is going to be slightly ambiguous, as context will always determine the answer. Every kind of IF can be good for health relative to other more deleterious dietary choices. That said, it is not always a healthy choice in every circumstance. Based on human research studies (most IF research comes from mice studies and can paint an overly rosy picture), there are two situations in which IF will be most beneficial to health:

1) When IF helps you sustain a caloric deficit and lose body fat

2) When IF helps you synchronize your circadian rhythms and sleep cycles (eTRF)

If you are employing IF by simply skipping breakfast and without considering important variables like protein intake and overall caloric load, your efforts to do something positive for your body could very well be hindering your health instead.

No problem, but if health and weight loss are your goals then you’re going to have to be well-prepared to ensure that your eating window is kept under 8 hours and fulfills the following:

• Adequate protein & nutrition
• A consistent caloric deficit
• Mindful choices in the evening hours, as to limit food volume and not impair sleep

• Better caloric control: As previously mentioned, IF can create a caloric deficit. If someone consistently sustains a calorie deficit, weight loss occurs with or without IF.
• Age: Healthy people under the age of ~30 will still have a hormonal profile with enough juice to drive relatively “easy” weight loss. As we age, hormones drop, and building muscle/losing body fat becomes more difficult.
• Hormones: It’s easier for men to lose weight than it is for women due in large part to hormonal differences.
• Activity level: Daily physical activity is an important precursor for health and helps drive weight loss.
• Stress management: IF tends to be a poor choice for people with high stress, as it can encourage dysfunction of stress hormone patterns and sleep.