WHEN you Eat can make you Fat

It’s nice when scientific research catches up with common sense.

For years, obesity experts have been telling us that losing weight is as simple as calories in v.s. calories out. But even the drunkest college co-ed knows that the calories she eats late at night after partying are going to end up as part of her Freshman 15. Even if she starves herself the rest of the day.

Human metabolism is much more complicated than calories in v.s. calories out. And science is finally catching up to this fact.

In a study presented this month at the Annual Meeting of the Society for the Study of Ingestive Behavior, researchers argued that “not only the amount and type of food eaten but the time of day it is eaten is important in contributing to obesity”.

Spurred on by previous studies which showed that when mice consumed all of their calories during their inactive period they gained more weight than when they consumed the same amount of calories during their active period, the researchers chose to investigate how “certain components of the diet, such as sugar or fat, contributed to differences in weight gain during different times of the day”.

The NEW Study

In this new study, the researchers gave rats either rodent chow or chow plus either saturated fat or a sugar solution. One group was allowed to consume the diets freely whereas the other groups were only allowed to eat either the fat or sugar during their inactive period.

They found that rats consuming all of their sugar solution in the inactive period gained more weight than rats consuming all their sugar solution during the active period, even though their total caloric intake was the same. They also gained more weight than rats consuming the saturated fat solely during the inactive period. The greater body weight gain in rats consuming sugar in the inactive period was associated with less heat production.

This research suggests that there are differences in the impact sugar drinking can have on body weight gain, depending on when in the day it is consumed.

For example, when you are sitting on your butt watching late night infomercials, your body doesn’t need food and will store away the majority of the calories you inhale.

Conversely, when you just finished doing one of my super-awesome Health Habits workouts, your body is primed to re-fuel muscle glycogen and begin repairing the micro-damage you just inflicted on your muscles. As well, your hormone profiles will make it highly unlikely that your post-workout calories will be stored as fat.

That’s why my ultra-lean clients eat the majority of their calories surrounding their periods of high physical activity.

It ain’t rocket science…but maybe it doesn’t have to be.


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  1. Interesting… I always eat ~300 cal snack about an hour before bed – during inactive time. Wake up starving if I don’t. I wonder if high EPOC counter-balances this effect?

  2. I think WHAT you eat before bed also plays a role – if I eat carbs before bed, I wake up ravenous – If it’s protein or even better…protein/fat, I have zero appetite upon waking

    EPOC could play a role, as would our own personal hormone profile / insulin and/or leptin resistance, etc

  3. I agree! I am for the first time here. I found this board and I find it truly helpful & it helped me out a lot. I am hoping to present something back and help others like you aided me. Fats consist of a wide group of compounds that are generally soluble in organic solvents and generally insoluble in water. Chemically, fats are triglycerides, triesters of glycerol and any of several fatty acids.  Fats may be either solid or liquid at room temperature, depending on their structure and composition. Although the words “oils”, “fats”, and “lipids” are all used to refer to fats, “oils” is usually used to refer to fats that are liquids at normal room temperature, while “fats” is usually used to refer to fats that are solids at normal room temperature. 

  4. Does anyone know whether the amount of brown fat in rats is different than in people?

  5. The pattern of brown fat loss from infancy to adulthood is similar between humans and rats. From individual to individual (rat to human – human to human, etc), the amount of brown (beige) fat is going to vary. If you’re really interested (and want to pay for it) there is a infrared style scan that can measure brown fat deposits

  6. I don’t eat carb’s- I do eat a load of vegetables (steamed) and fruit at night and snack on things like cherry tomatoes, carrots and cucumbers. I eat these things because I am so hungry at night! I also have a portion of protein at night with my evening meal.

    Is this the sort of thing that’s going to add weight? I have already cut down and have experimented with eating more in the day, but I still get really hungry at night and its annoying- I can’t sleep if I’m that hungry and so chomp on various vegetables/fruit.

    Is there a better way of doing this? I’d love to assume eating more protein helps but I have to say in my experience protein doesn’t seem to reduce my appetite. If the sugars from fruit and vegetables are making me put on weight then I’ve already lost my battle!

  7. Hey does anyone know why my boyfriend gets up in the middle of the night starving and usually heads straight for the peanut butter… He works out aerobically with high intensity most/all days of the week… ???

  8. I would look at the 3-4 hours before bedtime – specifically what and when is he eating prior to bedtime and how soon before bed is he training.

    This sounds like a blood sugar response?

    Is the PB all natural – just peanuts peanut butter, or the more commercial kind with sugar and palm oil?

  9. Hello!! I am wondering if you have seen the documentary Fat sick and nearly dead with Joe Cross …with his 60 day juice fast.If so, what do you think of the whole idea? I tried it for a couple of days but caved :/ I was also just going to try the 7 day fast

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