Meaning: 'Affect' means to have an influence on something, in this case, how hungry people feel based on their calorie intake timing.

Wrong options:

• defect: 'Defect' refers to a shortcoming or imperfection, which does not fit the context of influencing hunger.
• effect: 'Effect' is a noun meaning a result or outcome, which does not fit grammatically as the sentence requires a verb.
• collect: 'Collect' means to gather or accumulate, which does not relate to the context of hunger and calorie distribution.

Correct answer: filling

Explanation: The word 'filling' is an adjective that describes the act of consuming food that satisfies hunger. It fits contextually as it relates to the idea of eating a substantial breakfast, which is being discussed in the sentence.

Meaning: 'Filling' means providing enough food to satisfy hunger, making it relevant to the discussion of breakfast and weight loss.

Wrong options:

• firing: 'Firing' refers to the act of dismissing someone or the discharge of a weapon, which is unrelated to the context of eating.
• defiling: 'Defiling' means to spoil or desecrate, which does not fit the positive context of eating breakfast.
• compiling: 'Compiling' means to gather information or data, which does not relate to the act of eating or satisfying hunger.

Correct answer: observational

Explanation: The term 'observational' is used correctly to describe a type of research that involves observing subjects without manipulation. It fits grammatically and contextually as it describes the nature of the nutrition research being discussed.

Meaning: 'Observational' refers to a method of research where data is collected through observation rather than experimentation, which is relevant to the context of nutrition studies.

Wrong options:

• conventional: 'Conventional' means traditional or standard, which does not specifically describe the nature of the research being discussed.
• gravitational: 'Gravitational' relates to gravity, which is irrelevant in the context of nutrition research.
• disproportional: 'Disproportional' means not in proportion, which does not accurately describe the type of research being referenced.

Correct answer: regardless

Explanation: The word 'regardless' is an adverb that indicates that something is true without consideration of other factors. It fits grammatically and contextually as it emphasizes that calorie metabolism does not depend on the timing of consumption.

Meaning: 'Regardless' means without paying attention to the present situation; in this case, it indicates that calorie metabolism is unaffected by when they are eaten.

Wrong options:

• seedless: 'Seedless' refers to something that does not contain seeds, which is irrelevant in this context.
• priceless: 'Priceless' means something that is so valuable that it cannot be assigned a price, which does not fit the context of calorie consumption.
• emotionless: 'Emotionless' means lacking emotion, which is unrelated to the discussion of calorie metabolism.